While you have a point, in that the Blue Jays and Raptors have the benefit of no Canadian competition from coast-to-coast, your argument is also not necessarily strong.
There are a massive amount of people in Canada that root for teams like the Red Sox or the Mariners, and just as many bandwagoners that root for the Yankees.
Similarly, before the Raptors got good, I knew more Lakers fans in Toronto than I did Raptors fans.
You'd have a more convincing argument if the Leafs didn't also have one of the largest online fanbases of any team in the NHL.