You might consider YYC on KLM via AMS, or Westjet from London as in the Banff/Lake Louise area are a number of resorts - Norquay at Banff, Sunshine between Banff and Lake Louise, Louise, and Kicking Horse closer to Golden. A bit further south Fernie is a great resort, and generally warmer than the ones on the Alberta side of the Continental divide.

You'll find that accommodation and lift tickets should be cheaper than Whistler.