Wrong on both counts - the bar passage rate in NY for non-ABA JD holders is 36%, and the opportunities for advancement with a Canadian degree in the American market are extremely limited - basically you can get in, maybe, but you're certainly not going to move up quickly, if at all. If flexibility is your top criterion for choosing, then the US wins hands down. Not to say that there aren't other good reasons for staying in Canada for a lot of people, though.
By flexibility, I'm talking about working in either jurisdiction. It is undeniable that a Canadian llb gives you more immediate options in the US, than a US JD gives you in Canada, simply because of the policies of the various provincial bar associations. A person cannot graduate from USD and write the bar in a Canadian province. McGill, U of T, and Osgoode are all recruited by V100 US firms, and send 30 students between them to NYC firms. I don't know what you're talking about when you say "moving up", because no one "moves up" at these firms until they make partner. I don't see why firms like Cravath and SullCrom and Skadden would take a couple of Mcgill and U of T students every year, and actively recruit on campus, if it was impossible for them to "move up."
Nobody's saying it's impossible, it's just extremely difficult because you won't have the same connections as others within the markets where you practice. Let's remember that the ONLY TWO jurisdictions that accept Canadian degrees as equivalent for the purposes of writing the bar are NY and MA - that's it. If you want to go to California (for example), you would have to first pass the bar in either one of NY or MA (again, difficult, given the 36% bar passage rate for non-ABA approved degree holders, and yes, that includes everybody who takes it who does not have an ABA JD including Canadians and including U of T students), and then move to go through the same process in the other jurisdiction. Again, you would still face the same barriers given the fact that you wouldn't have the same connections - it would be the same for a US lawyer coming to practice in Canada. Connections mean a lot in the legal world.
While it might be slightly easier to go with a Canadian degree to the US, the US JD (especially top-ranked) is more recognized internationally and will (with some work) get you a decent job in Canada.
Come on, 30 students between the three schools in NYC, and you say that's evidence of Canadians moving up in the US market??? That's laughable - there are literally hundreds of students that go to NYC for their first jobs as associates every year, merely 30 students between three of the top Canadian schools does not mean that you will have huge opportunities to move up, believe me. Additionally, that figure (if true), only further goes to show that while some firms may recruit in Canada, lots of people don't want to go to the US and the firms won't go as deep into the classes.
I agree, though, if you want to practice in the US for any time at all, study in the US, and vice-versa if you want to practice in Canada. . .