I don't have the exact stats, but something on the order of 6-7 of the 30 or so McGill students who entered the American match this year matched to a Harvard program. Historically, approximately 90% of McGill grads get their #1 choice residency.
While neither of these statistics fully answer the original question, I think you can rest assured that attending McGill will not limit your residency options. Whether McGill is on par with Harvard, Columbia, UCSF, etc. as opposed to NYU, Rochester, Emory (with regards to reputation) is anyone's guess.
I fully agree with everything redpoint mentioned, as well.