when I went to Whistler last year, I was concerned about the same thing, just check your bag inside and you should be fine. The airlines told me that specific bags, like hockey and ski bags were not typically charged extra (so long as they were one of the two bags being checked, like said above, if its a 3rd bag you'll pay).
BTW the bag I brought had 4 pairs of skis, 4 pairs of poles, and clothes and towels in it.
Also something to note, that I kinda paniced about when they swabbed my ski bag, ski wax, although it is an accellerant and flamable (and combustable too I thought) was not a problem when they swab the bags for chemicals. When they swabbed it, I kinda paniced since I knew there was wax particulate (and acetone) all over my bag, and she said it wasn't a problem.