I'm all for the real working Canadians (BC, Albera, Manitoba, Saskatchewan maybe, to join the US. As to the Mexican provinces, I'd take Baja, but nothing else, and I'd fortify the border: I grew up in California and have seen it destroyed by illegal immigration. No thanks to a population of Mexican Indian peasants. Sorry.
Oh, I agree, I'd just move the fortified border 200 miles South.