A guy from my school applied last year to McGill with predicted 37 and got an essentially unconditional offer of just 28 points.
That was the case for a lot of the people at my school applying to canadian unis, they were predicted A LOT higher than the offers.
Another guy however applied to McGill (two different courses there) and didn't get into either and he was predicted decent points, mid 30s if not higher and didn't get in to either course. He didn't apply early due to administrative problems at our school and a lot of the documentation got lost in the mail, so I think this played a large factor in being unsuccessful.
From what I've understood, Canadian unis base offers entirely on predicted grades and not on personal statements or references as theyre not required, which in lots of ways makes it harder to differentiate between candidates, as you can tell a lot about a person by their PS.
BTW, I think for most courses, you have to take Math SL rather than studies (check before applying!)