I tore my MCL, and was skiing on it (but only on the bunny hill with my wife) that week, and (not on the bunny hill) ten days later, in a brace, but was probably mostly lucky along with (insert appropriate euphemism for unwise.) Didn't reinjure it (walking was much more painful than skiing) but I skied a lot less aggressively than usual and had one fairly terrifying run down one of the back bowls of Vail in poor snow conditions where I was just sure I was going to hook the inside edge of the bad leg and tear my knee apart. (I didn't, but it was an interesting lesson on how fear can affect balance.) Especially at Whisler, with its variable snow conditions, consider trying to stay on the part of the mountain with better snow.
In the initial phase, as suggested by my physical therapist, I did a lot of range of motion exercises, trying to completely straighten the leg and bend it completely, so that, despite scar tissue, I'd get full range of motion back. That hurt (especially initially with the swelling) and ice and ibuprophen were helpful. In the later phase (maybe, after six weeks?), I did a lot of general strengthening exercises for all the muscles around the knee.
Talk to a good physical therapist. Talk to a good sports medicine doctor, or a ski town doctor with experience in this. Take their advice over everything mentioned below.
Even after you get rid of the bulky hinged brace (wouldn't really want to fall hard on that one) you might consider putting an elastic brace on the knee. I'm not sure it has any therapeutic effect, but it works well psychologically, to keep you aware of the knee and to restrict deep knee bends and knee angulation.
It you're still wearing the bulky hinged brace, wear it on the inside of your ski clothes. The doc at Park City told me the skiers wearing them outside the ski clothing might as well not wear them at all, for all the good they do there.
Don't ski the more challenging stuff--you really don't want to reinjure it (or your meniscus or your ACL.)
Look at chairlift height off the snow at loading--for me, the most painful thing (and pain is your body's way of saying don't do that) was deep knee flex necessary to sit in the lift where there was limited ground clearance at loading.
As LisaMarie suggests, avoid the knee extension machine in favor of light closed chain exercises. (And, IMHO, the knee extension machine should be avoided even by healthy people in favor of exercises like squats and lunges that are more real world applications.)
In general, ice and ibuprophen are your friends. If the knee is sore after a workout or skiing, ice it, to reduce inflammation.
Finally, pay attention to your walking gait as you recover. I ended up with a toe-out walk on the hurt leg that made my knee hurt in other ways until I realized it and made a conscious effort to correct it and walk with the foot pointed straight.