I do believe tho, having spent a lifetime moving back and forth across the border at Detroit, that it is highly unlikely there were ever be a scenario where Americans support the annexation of Canada against Canada's will.
It would be different if it was a willing compact. We like Canadians a lot and think of them as more a brother than a neighbor.
But I do genuinely believe there would be a response, if Trump took over Canada by force. Enough of a response to stop it? That I am unsure about.