I presume you already looked at the historical cutoffs on McGill’s web site? Requirements for U.S. applicants | Undergraduate Admissions - McGill University
For Arts, last year’s cutoffs are listed as:
- 3.3 average (unweighted) in each of grades 11 and 12
- B+ in each English
I don’t know exactly how to translate your numbers to letter grades as this can depend on the HS, but it might appear on your HS transcript or your school profile.
As far as when you hear back from them, generally they want to see senior year grades from the first marking period (plus all your other HS grades). Once they get all that info, you might see a decision any time, but the timing varies a lot.