The best time to ski in Canada is during Thanksgiving. It is not a recognized holiday so the schools are in session and everyone is at work. It's considered off season so lift tickets are very cheap. Most resorts are open and there will be plenty of snow.
Lake Louise is a beautiful resort and very expensive. Just stay in town and drive the ski areas.
We honeymooned at Lake Louise. Highly recommend the Chateau. We skied Lake Louise. Resort was nice. Skiing in Canada is not for wimps though. It gets cold!
Have skied lake louise and sunshine extensively (grew up in Calgary)...I'd split between the 2 if you have enough ski days. Only about 45 minutes apart or so to my recollection so easily drivable wherever you are staying. Sunshine typically has better snow and is back in it's own bowl. Lake Louise is spectacular with the panoramic views and personally I like the runs better. I would say Lake Louise has more beginner terrain to explore with wide cruising runs.