The rule used to be much stricter. As in, *no* Canadian schools.
The NCAA opened up a pilot program in 2008 that allows Canadian schools to join the NCAA at the Division II level. Only one school (Simon Fraser U, in Burnaby, BC, right next to Vancouver) has taken them up on it so far.
But as far as D-I, it is presumably the case that anyone can join if they meet the D-I requirements, but because of the D-II membership rules, the school must join D-II for at least a small amount of time before qualifying for D-I membership.
Or, to put it another way: if we tried to convince UToronto or any other school to join D-I to get into the AAC, we're looking at a minimum of ten years before that school *actually* competes in the AAC.