Why would we give Canada California (Canadians probably wouldn’t want it anyway) then join? Invade/conquer? Canada; who most definitely wouldn’t want to join our federal government. No matter how good we have it or bad they have it. It’s the one thing we agree on, our federal government sucks!
Plus, if the endgame is to annex Canada, whatever you think that means, we can do that now.
I’d argue it makes more sense to annex Mexico. So we can better control what comes in from South America. However, annexing any country will lead to war.
Good luck with selling that idea!