I'm at mcgill and im from MA as well, for the record bromont kicks wachusetts ass from opening day to closing day.
from what i understand mcgill only looks at jr/sr year. given that, i had all b+/a in all ap/honors from then on and got waitlisted on my top (engineering) choices, but was given other (engineering) programs i could go in for. everything obviously depends on the faculty you apply into, and as i'm sure you know the application is strictly a judgement of your academic record nothing else.
and yeah, its no harvard, if you wanna apply to canada in general i'd send apps to UBC, UT, Queens as well as i did. UT and UBC if I remember correctly are just as easy to apply as mcgill and just care about grades. at the end i chose mcgill because 90% of americans have heard of nothing other than mcgill and i don't plan on working in canada after. oh, and montreal is prolly the best place to spend your college years.