Canada-Mexico can't do it alone, but
A) We're great for the Europeans to launch an attack from. Especially Canada as the border is really just an easy to remove fence.
B) Mexicans could just walk in across the border and welcomed by the dems..
C) If America has a civil war, we could team up and become the king maker. This sort of happen during the American civil war, we supported the Confederates(via Britain) because we wanted that cotton. The reason Canada became a country is in no small part because we got scared when the Union won. The country started in 1867 and the work to build one was almost immediately after a union win.