I think the English speaking part of Canada would actually like their own country. Nothing against the US but I don't think a "take over" would sit well.
If Canada breaks up, the U.S. should certainly not try to force any of the provinces to join the U.S. Anyway it's doubtful that it would be in our interest to have any part of Canada added to the U.S., except maybe Alberta. Canadians tend to be more liberal than Americans so adding them to the U.S. would only benefit the Democratic Party.
David H. Wilkins, the new U.S. ambassador to Canada (a South Carolinian) was on C-SPAN recently. He sounded like a good man for the job.