I think a big part of it is that canadian students are less likely to apply for American schools. It is expensive to apply, expensive to attend and difficult to come back. If you check out lawstudents.ca, there are a few people who think they may stay at UofT even if they do get into top american schools. Cheeks was debating (but is now at Harvard).
That being said, they take most of their students from the HYPSC set, which us Canadians could have attended. So I think just not going to those schools is an issue.
Still, good grades, lsat and experience should get you in. I hope to be the first from my school to get in!!