How many people will be going to Japan in your ski club? If it's a decent sized group of you, I'd pick Japan.
You can always make friends inside the group, even if you only know a couple people at first.
Japan is one of those things that should be done in a group because it makes it infinitely more fun. Especially once you engage in apres.
Whistler is amazing, but the feel isn't that different from other big resorts in N. America. It's got amazing terrain and something for everyone, but it's more of what you may have already seen.
Japan is a totally different experience, both snow and culturally. It's not something you get in a lot of other places. You can always go to Whistler another time since it's insanely popular with basically everyone in N. America.