And what of the third largest metro area north of the Mexican border?
I don't think a team other than the Bills moves to Toronto, and my guess is that they don't. The Bills don't own Toronto the way they think they do: the "popular" teams like the Pats, Steelers, and Niners are just as popular in Toronto.
They
could though, first by just improving on the field. The new stadium will be a draw for Toronto fans, especially if it ties into Niagara tourism, or is just a cool place downtown. The proposed site between Buffalo and Rochester is a bad idea, IMO.
I believe Canadian NFL broadcasts are divided between broadcasters according to time slots (1pmET/SNF/MNF vs. 4pmET/Thursday) so it's hard for either network to "own" the Bills (though the former gets most of their home games).
One thing that could work well in Toronto is a London-type situation where they rotate teams. But personally I like home teams to keep their home games...