Canadians scoring highly on the LSAT do not necessarily wish to go to Toronto. Canadian schools tend to be more regional as a whole than top US law schools. I did not even consider applying to law school in Toronto, for example. (I did not apply to any Canadian schols, but if I had, it would have been to UVic and UBC.)
I would also believe that Canadians scoring highly on the LSAT are more likely to attend top American law schools, further reducing the pool of 170+ applicants to schools like Toronto.
I doubt assertions that Canadians as a whole are not as good at standardized tests as Americans, merely due to the lack of an SAT or ACT to enter into undergrad.
Can I ask why you want to go to school in the U.S.? Are you planning to practice there and if so how are you going to deal with the immigration issue?