thumb|U.S. states and Canadian provinces and territories

Various individuals and movements within Canada and the United States have campaigned in favour of U.S. annexation of parts of or all of Canada or have predicted it without endorsing it since their common origin as parts of British America. Before the United States even declared its independence, there were efforts to have parts of what is now Canada join the Thirteen Colonies in their complaints against Great Britain. American forces unsuccessfully attempted to invade Canada during the Invasion of Quebec of 1775 and War of 1812. One last American diplomatic effort to annex Canada was made in the aftermath of the American Civil War and confederation of Canada, but the 1871 Treaty of Washington did not include any such provisions.

Various groups and individuals in what is now Canada have campaigned for part or all of Canada (earlier, British North America) to join the United States, generally over opposition to British rule or the Canadian federal government. After a spike of interest, they have faded into obscurity, often after their concerns were addressed within the existing system. Historian Joseph Levitt is quoted in a 1993 book as saying:

Surveys have suggested that a minority of Canadians would potentially support annexation, ranging from as many as 20 percent in a survey by Léger Marketing in 2001 to as few as seven percent in another survey by the same company in 2004. One poll in the 2020s, noted by the Toronto Star, showed that about 50% of Americans are against Canada joining, 25% are in favour, and 25% are not sure.

After winning a second term as president in the 2024 election, U.S. president Donald Trump said Canada should become the 51st state of the United States. Canadians responded strongly against these calls, with Prime Minister Justin Trudeau saying, "There isn't a snowball's chance in hell that Canada would become a part of the United States".

Canadian annexationists

Historical annexationist movements inside Canada were usually inspired by dissatisfaction with British rule in Canada. Despite some unrest, opposition to British rule never reached the degree that led to the American Revolutionary War in 1775. Notably, Canada's population growth in the late 18th and early 19th centuries was spurred largely by United Empire Loyalists, who left the American colonies during the Revolution because of their loyalty to Great Britain. In the period from 1790 to 1837, imperial officials repeatedly denounced American-style republicanism and tried to suppress it.

1837

Groups of Irish immigrants took the route of armed struggle, attempting to annex the peninsula between the Detroit and Niagara Rivers to the United States by force in the minor and short-lived Patriot War in 1837–1838. Not all rebels desired union with the United States; some fought for an independent nation state or for liberal social reforms.

1840s and 1850s

Between 1848 and 1854, a significant and articulate minority of conservatives in Upper Canada advocated constitutional changes modelled on the American federal-state system and the US Constitution. They critiqued Canada's imitation of British parliamentary government as simultaneously too democratic and too tyrannical. They believed it destroyed the independence of the appointed governor and Legislative Council and further concentrated power in the Cabinet. This critique led many conservatives to argue that the American model of checks and balances offered Canada a more balanced and conservative form of democracy than did the British parliamentary government. These "republican conservatives" debated a series of constitutional changes, including annexation to the United States, an elected governor, an elected Legislative Council, a federal union of British North America, and imperial federation, within this framework. These conservatives accepted "government by discussion" as the appropriate basis for political order.

In midcentury Montreal, with little immigration and complaints that the repeal of the Corn Laws had cut the region off from its British trade links, a small but organized group supported integrating the colonies into the United States. The leading organization advocating merger was the Annexation Association, founded in 1849 by an alliance of French Canadian nationalists and Anglophone businessmen in Montreal who had a common interest in the republic. Many of its members, including Louis-Joseph Papineau, were participants in the 1837–38 rebellions.

The Montreal Annexation Manifesto was published in 1849. It was hoped a merger with the United States would give Canada markets for its goods, ensure national security, and provide the finances to develop the West. A half measure was the Canadian–American Reciprocity Treaty of 1854 that linked the two countries economically. However, the movement died out in 1854. Annexation was never a very popular choice. Many Canadians were loyal to the Crown and Great Britain, especially the descendants of the United Empire Loyalists. French Canadians worried about being an even smaller minority in a larger union, and were concerned about American anti-Catholicism.

Around 1850, there was a serious annexationist movement on the border region of Quebec's Eastern Townships, where the American-descended majority felt that union with the United States would end their economic isolation and stagnation as well as remove them from the growing threat of French Canadian political domination. Leading proponents of this bipartisan movement were careful not to appear disloyal to Britain, however, and they actively discouraged popular protest at the local level. Fearful of American-style democracy, the local elite also expressed revulsion toward American slavery and militaristic expansionism. Consequently, the movement died as quickly in the Eastern Townships as it did in Montreal after Britain expressed its official disapproval and trade with the United States began to increase.

1860s

William Seward, subsequently Secretary of State under Abraham Lincoln, predicted in 1860 that western British North America, from Manitoba to British Columbia, would join the United States along with Russian Alaska. Many in Britain, such as Goldwin Smith and The Times of London, were pessimistic about the future of British North America and agreed with Seward; The Times said that Britain would only object if the United States attempted to take the territory by force. Most Canadians were strongly opposed to the prospect of American annexation. Reports of the Annexation Bill of 1866 — a bill introduced in the U.S. House of Representatives that, contrary to myth, never came to a vote — might have been one of the many factors behind Canadian Confederation in 1867. Much more serious were the Fenian raids made by Irish Americans across the border in 1866, which spurred a wave of patriotic feeling that helped the cause of Confederation. The American Civil War further convinced many Canadians that the American experiment was a failure.

British Columbia

thumb|Map of North America in 1864

In the late 1860s, residents of the Colony of British Columbia, which was not yet a Canadian province, responded to the United States' 1867 purchase of Alaska with fear of being surrounded by American territory. Some residents wanted the colony to be the next American purchase. Local opinion was divided, with the three Vancouver Island newspapers supported annexation to the United States, while the three mainland newspapers rejected the idea. Even opponents of the annexation scheme admitted that Great Britain had neglected the region and that grievances were justified. Nonetheless, annexation sentiment largely disappeared within a few months, and prominent leaders moved toward confederation with Canada.

Petitions circulated in favour of American annexation. The first, in 1867, was addressed to Queen Victoria, demanding that the British government either assume the colony's debts and establish a steamer link or allow the colony to join the United States. In 1869, a second petition was addressed to President Ulysses S. Grant, asking him to negotiate American annexation of the territory from Britain. It was delivered to Grant by Vincent Colyer, Indian Commissioner for Alaska, on December 29, 1869. The petitions were each signed by only a small fraction of the colony's population, and British Columbia was ultimately admitted as a Canadian province in 1871.

Nova Scotia

thumb|Map of Nova Scotia

Despite the general opposition, a substantial annexationist movement existed in Nova Scotia, and to a lesser degree in New Brunswick, Quebec, and Ontario, during the 1860s. Nova Scotia anti-confederationists led by Joseph Howe felt that pro-confederation premier Charles Tupper had caused the province to agree to join Canada without popular support. Howe in London unsuccessfully attempted to persuade the government to free Nova Scotia from the pending British North America Act by threatening American annexation. A significant economic downturn occurred after the 1866 end of the Reciprocity Treaty of 1854; the colony was heavily dependent on selling fish to Americans, causing many to believe that free trade with the United States was necessary for prosperity. Anti-confederationists won all but two seats in the 1867 provincial election; as in British Columbia, they did not necessarily support annexation. They again sent Howe to London to free Nova Scotia, but in 1868 the British government again refused, believing that New Brunswick would likely follow Nova Scotia out of the dominion and cause the new nation to collapse.

Angry Nova Scotians began talking seriously about annexation. An alarmed Howe — who wished Nova Scotia to be free of Canada but still with Britain — warned his supporters against disloyalty, dividing anti-confederationists. The provincial government, dominated by extremists who now also opposed Howe, decided that if another appeal to London failed, it would seize federal offices and unilaterally declare annexation, believing that Britain would not use force to stop the province. Believing he had no choice, Howe left the anti-confederationists. Although he narrowly won reelection to his federal parliamentary seat in March 1869 as a confederationist, support for secession and annexation grew that year. The federal government promised changes to taxes and tariffs, the economy was revived, and the United States agreed to free trade for Canadian fish. By 1871, the movement had mostly disappeared.

1880s

A Quebec-born homeopathic physician, Prosper Bender, expressed disappointment with the Canadian experiment in the 1880s and 1890s. An author and the former host of a literary circle in Quebec City, Bender suddenly moved to Boston in 1882. After celebrating the promise of Confederation, he became a strong proponent of annexation to the United States and something of an intercultural broker; he helped interpret French-Canadian culture to American readers. Bender wrote in the North American Review in 1883 that many Canadians believed that annexation by the United States would occur "within the present generation, if not sooner". He believed that Irish Catholics — about one-quarter of Canada's population — would prefer annexation because of British rule in Ireland. They would be joined by the majority of those under 40, who viewed the United States as a prosperous, fast-growing neighbour providing many opportunities. He attributed the absence of an active annexationist movement in part to many who would favour such an effort taking the "easiest and quietest method of securing the benefits of annexation, by themselves silently migrating to the Republic", as more than a million already had.

Bender believed that Prime Minister John A. Macdonald's promise of a transcontinental railway linking eastern Canada to British Columbia to be overambitious and too expensive, and unfavourably compared the Canadian government's growing debt to the United States' rapid reduction of its Civil War debt. He stated that Canadian businesses would benefit from duty-free access to the American market, while "wondrous American enterprise, supported by illimitable capital" would rapidly prosper Canada, especially its vast undeveloped interior. Bender concluded with pessimism about the likelihood of success of a nation divided into two parts by 1,200 miles of "forbidding, silent wilderness stretching from the head-waters of the Ottawa to Thunder Bay, and thence to Manitoba".

1890s

In 1891, Goldwin Smith posited in his book Canada and the Canadian Question that Canada's eventual annexation by the United States was inevitable, and should be welcomed if Canadians genuinely believed in the ideal of democracy. His view did not receive widespread support.

In January 1893, concerned about Canada's possible annexation, a goal then being pursued by the Continental Union Association (a group of Ontario and Quebec Liberals), Prime Minister Sir John Thompson delivered a speech on tolerance, Canadian nationalism, and continued loyalty to Britain. Thompson eventually learned that the desire to make Canada part of the United States was confined to a small minority amongst the Liberals.

1900s

In 1901, W. T. Stead, a newspaper editor in London, England, discussed in The Americanization of the World possible annexations of Canada and Newfoundland. He believed that because of its size and strength, Canada would likely be the last of Britain's possessions in the Americas to join the United States. Stead cited several reasons for why he believed annexation seemed "inevitable", including rapidly growing economic ties and migration between the two countries, the French Shore, and disputes over the Alaska boundary and fishing rights in the Atlantic.

After the discovery of gold in the Yukon, many Canadians proposed to annex parts of Alaska currently controlled by the United States, by calling for a revision in the original map of the boundary line between the Russian Empire and the United States. The United States offered to lease the territory to Canada but not to give it back. London and Washington agreed on arbitration, with one member of the panel from Canada. In 1903, the Chief Justice of Britain sided with the Americans to resolve the map dispute in favour of the United States. Many Canadians felt a sense of betrayal on the part of the British government, whose national interest required close ties to the United States regardless of the interests of Canada.

1930s

The 1932 establishment of the International Peace Garden on the North Dakota–Manitoba border honoured the long-lasting friendship between the two countries rather than attempts at annexation.

Newfoundland in the late 1940s

While the Dominion of Newfoundland was still separate from Canada, before 1949, a party known as the Economic Union Party (EUP) sought closer ties with the United States. However, Canada objected to the possibility, and the British government, which administered the Dominion of Newfoundland as a de facto colony under an appointed Commission of Government, would not allow it to consider annexation with the United States in any referendum. Instead, the EUP sought to resume "responsible government" and would then explore American annexation. A referendum showed a plurality in support of independence, but not a majority; a runoff referendum resulted in Newfoundland instead confederating with Canada to become the tenth province.

1980s

The Unionest Party was a provincial political party in Saskatchewan in 1980 that promoted the union of the western provinces with the United States. It was the most politically successful annexationist group, but its success was both short-lived and extremely limited in scope. The party briefly had two members in the Legislative Assembly of Saskatchewan, both of whom crossed the floor from another party, but dissolved within a few weeks after failing to qualify for official party status.

The original Parti 51 was a short-lived political party in Quebec in the 1980s that advocated Quebec's admission to the United States as the 51st state. The party won just 3,846 votes, or 0.11 percent of the popular vote in the province, in the 1989 election — fewer votes than the Marxist–Leninists or the satirical Lemon Party — and was dissolved the following year.

21st century

Two modern provincial political parties have proposed that their province secede from Canada and join the United States. Neither attracted significant support. A 2022 poll showed that fewer than one in four Albertans support separation from Canada.

In 2016, Hans Mercier, a pro-American lawyer from Saint-Georges, Quebec, revived Parti 51. Mercier told La Presse that the times have changed since the party's previous era, as Quebec sovereigntism has waned in popularity. Mercier argued that Americans would be welcoming of a new Quebec state, and pointed to a survey taken during the administration of George W. Bush that suggested nearly 34 percent of Quebecers would support joining the United States. The revived party ran five candidates and received just 1,117 votes provincewide in the 2018 Quebec general election, representing 0.03 percent of the provincewide popular vote. The party ran again and received just 689 votes provincewide in the 2022 Quebec general election, representing 0.02 percent of the provincewide popular vote.

Albertan annexationism

Alberta separatists have proposed several paths, one of which is joining the United States either as a territory or state. However, few among Albertan secessionists support actual annexation.

The most vocal group in Alberta advocating for annexation to the United States is the Alberta 51 Project, founded in 2023. Among the group's stated goals are the elimination of customs barriers, a stronger military presence, the protections of the US Constitution, enhanced protection for land and resources, and economic stability through the U.S. dollar. During an event in Calgary where American political commentator Tucker Carlson spoke with Alberta Premier Danielle Smith, members of the Alberta 51 Project staged a minor demonstration. Demonstrators displayed signs and a Trump 2024 campaign flag in support of Alberta annexationism.

Alberta during Trump's annexation proposals

thumb|Alberta premier [[Danielle Smith|227x227px|left]]

Initially, Premier Danielle Smith believed that Trump's comments about annexing Canada were made in jest. However, amid escalating trade tensions between Canada and the United States following Trump's annexation proposal, Smith refused to endorse a retaliatory response to U.S. tariffs imposed by Trump. Instead, Smith advocated for increasing U.S. purchases of Alberta oil and rejected measures such as curtailing, suspending, or taxing energy exports. This stance placed Smith at odds with the federal government and other premiers across Canada.

On January 12, 2025, Smith set up an impromptu meeting with Trump at his Mar-a-Lago residence in Florida, as a guest of Canadian businessman and television personality Kevin O'Leary, discussing U.S.-Canadian energy relations. After she met with Trump, Smith warned that blocking energy exports to the U.S. in response to Trump's tariff threats could lead to a "national unity crisis" in Canada, as the provinces primarily own oil and gas resources, and that such a move by the federal government would not be tolerated in Alberta. She also remarked that if the federal government proceeded with an export ban, she could not "predict what Albertans would do". Smith expressed to other premiers that she was committed to safeguarding the livelihoods of Albertans from "destructive federal policies". Smith remained noncommittal, refraining from taking a definitive stance on the issue of annexation.