For Class IV-V in the Whistler area the Soo, Cheak, and Callaghan will be your best bet...but they are forecasting even more rain in the area--significant amounts that will jack things up even more.
You can check the weather page here:
Squamish, British Columbia - 7 Day Forecast - Environment Canada
There are pretty good runs on the Seymour and Lynn Canyon in North Vancouver if stuff in Squamish/Whistler is too high.
You could also ask the locals about Norrish Creek and other runs out near Chilliwack/Abbotsford.
Have fun up there!