The Montreal Annexation Manifesto was a political document dated September 14, 1849 and signed in Montreal, Quebec, calling for Canada's annexation by the United States.
The Manifesto was published in two versions (October 11, 1849 and December 1849) by the Annexation Association, an alliance of 325 Montreal businessmen (mostly English-speaking Tories), who were opposed to Britain's abolition of the Corn Laws, thus ending preferential colonial trade, and by its consent to the Rebellion Losses Bill, and French Canadian nationalists (including Louis-Joseph Papineau) who supported the republican system of government in the United States. These businessmen believed that so long as the Provinces of Canada were under British rule, it would be subjected to the interests of elements of Britain's aristocracy and businessmen. Papineau too had believed a similar subjection occurred, perpetrated by France and, given the tiny population in Canada compared to that of the United States, these people believed that the abolition of customs duties at such an early point in Canada's economic development would be disastrous for Canadian business and the job losses would be massive.
The Manifesto was strongly opposed by members of the British American League and by leading politicians such as Robert Baldwin plus the followers of Louis-Hippolyte Lafontaine. After the signing of the Canadian–American Reciprocity Treaty in 1854, the Annexation movement died out.
In an editorial, the New York Herald newspaper responded to the Annexation Movement with the following advice: "The first thing for the people of Canada to do, however, is to obtain England's consent to dispose of themselves as they think proper."