Alas for the maritimes, their economies were exclusively dependent on the seal and cod fisheries, both of which are long moribund. Alaska and Hawaii were only admitted simultaneously to the union because one was reliably Republican and the other reliably democrat. This is why the District of Columbia and Puerto Rico will achieve statehood when pigs learn to fly. I cannot imagine the sort of "Missouri Compromise" that would be necessary to take on any part of Canada but it sure seems unlikely that both parties could somehow divide it up equally. I do not see as we could afford to take on territories as our one and only colonial venture one hundred and five years ago (Philippines, Cuba and PR--Spanish American War "booty") is still costing us (Thomas Sowell went into some detail in one of his books how europe's vast colonial empires amounted to a lot of red ink when the pros and cons were added up). Canada will have to solve it's own problems. We can't afford it.
Canada and Mexico as they presently exist must be destroyed-their national sovereignty is too robust to enable us to prevent their use as terrorist bases.
An emasculated Lower Canada, absorbtion of the West, free Quebec behind American guns and with basing rights, and Mexico driven beyond Veracruz will be much safer for us-and better for the lucky Mexicans and Canadians we take in.