well, as long as you don't mind missing out on whistler from may till august (kiss summer camp goodbye) seasonal bush jobs are pretty much the bees knees.
treeplanting and forest fire fighting are the two main money makers.
planting goes from late april till mid october. Well, planting starts in mid february, but who the fuck wants to plant trees in february? getting a job in the planting world is easy, just do your homework as to which company you are giving your summer to.
fire fighting is harder to get into, but if you can get a spot on a crew and the summer is good (good meaning lots of fires) you can work from may till november and pull in mad cash. my gf's room mate pulled in 22g after taxes last summer. unfortunately this summer wasn't very profitable and he only made around 10g.
the bonus with these jobs is they lay you off at the end of the season, and you've almost always banked enough hours to go on EI for the winter after.
I guess you could always be a bartender or server at a high end restaurant in a ski town and get mad tips - but how many positions are available for that? probably not enough to count on it i'd think.