I also got my rejection letter from McGill today and was feeling pretty down about it as well. It's definitely tough when you feel like you have a such a solid application. The competition is really tough! I wouldn't lose hope yet though because I've heard Western tends to take a more holistic look at applications. So what they may be looking for at McGill might not be what they're looking for at Western.
Also, someone correct me if I'm wrong, but I think McGill actually looks at cumulative GPA as well as subGPA when making admission decisions whereas a lot of other schools only look at subGPA. So if you had a lower cumulative GPA that may have played a role.