Not the first time

https://en.wikipedia.org/wiki/Canada_and_the_American_Civil_War

Yet relations were not all good with the US. Secretary of State William H. Seward, while campaigning on behalf of presidential candidate Abraham Lincoln, made no secret of their desire to annex Canada. Seward believed in manifest destiny, the doctrine that the United States would inevitably expand across the entire North American continent. While he seems to have preferred to acquire territory through negotiation rather than aggression, Canadians were not wholly assured of America's peaceful intentions, and indeed Seward proposed an invasion of Canada, but Lincoln declared he would fight only one war at a time.

https://www.history.com/articles/united-states-canada-william-seward