Spawned out of an IRL discussion. It's pretty insane, and probably done already, but for some reason I'm really curious. For one reason or another, the American government decides to invade Canada. They can take as long as they want to prepare and carry out an invasion. The current administration and sufficient Congress members to form a government (do you need Congress to declare war? In Canada the House of Commons must vote on it) support the war, and the military is assumed to follow orders like they would any other. The objective is to annex Canada and make it part of the United States, so capturing Ottawa isn't enough and genocide is too far. Tactically and strategically, how would an American force go about invading Canada? What kind of defence could the Canadians put up? How would the public react on both sides of the border? How would the international community react?