I skied Big White, Silver Star, Apex plus 2 days cat and one heli in Revelstoke in February of the epic 1999 season. Lots of snow and only 1/2 day of sun in a week.
I have snow stats and analysis of Big White and Silver Star at
http://bestsnow.net/crocnet.htm . If you're there a week you should probably try all 3 Okanagan areas.
Big White is high altitude by B.C. standards but the main part of the area faces south. The steeps face east and the long Gem Lake chair faces west and goes lower than the main base. There was not even a hint of spring conditions during my visit due to ongoing snowfall and chronic fog/overcast (thus the nickname Big Whiteout).
Silver Star is lower and gets less snowfall. The steep Putnam Creek backside has similar elevation range as Fernie but it does face north and is less likely to get rain.
The front side of both areas will have instant spring conditions if the sun comes out in March due to south exposure. Most of this terrain is intermediate and groomed though.
I only got to ski about 1/4 of Apex's terrain due to the weather closing the main lift. Snowfall is lower than Silver Star but main exposures are north and east.
In late March/April Sunshine Village, the backside of lake Louise and the Whistler alpine have the best odds of packed powder conditions in western Canada. Also the upper elevations at Panorama and Kicking Horse, though those areas have other concerns.
