Canada has some mountains that are known for great powder skiing, but the real powder Meccas in North America are in the United States.
Canada does not have many resorts that average 400 inches or more of snow. Our snowiest hills are Whitewater, near Nelson, and Shames and Powder King in the north. I really like Whitewater, but it is kind of small. Many locals use it to access great backcountry skiing. I haven't been to Northern BC, but these "resorts" also seem to be backcountry launching places.
Other resorts that receive a fair bit of snow include Revelstoke, Fernie and Whistler. Whistler actaully gets a lot of snow, but it can be wet and competition for powder is feirce. Fernie has had some epic seasons, but many seasons aren't that spectular. Rain can be an issue at Fernie, and their avalanche situation is tricky----meaning the best terrain is slow to open up. I haven't been to Revelstoke (yet) but it seems as though elevation could be a minor issue.
Red, Castle, and Kicking Horse get a resepectable amount of snow, and competition for it is pretty light. Casle is high and cold enough to avoid most of the rain that Fernie gets. It is virtually deserted midweek, and won't get skied out on the weekends. Kicking Horse can be a solid choice as well. Red's stashes can last for days, but it's low elevation makes rain a concern.
The Okanagoan Resorts have reliable snow, but their stats aren't that impressive. I tend to view Big White, Sun Peaks and Silver Star as "family" resorts.
It never snows at Panorama.
The Alberta areas, apart from Castle, are also quite dry.
While there isn't a perfect powder destination, the snow can be really good if you time it right. If I was planning a trip to Canada to ski powder I would choose between 4 areas:
I don't know if Whistler has cat skiing nearby (they have Heli for sure), but the other resorts are near great catskiing ops.