I just drove through Banff National Park on Monday night. There was LOTS of space in the Lake Louise overflow. Keep in mind that it is just a gravel parking lot with no services. Even though it is close to the highway, it is probably quieter than the main Lake Louise campground as it is right beside the railway tracks.
Also, you can get spots in some of the other campgrounds during the week as long as you don't mind moving every night or two.
The Parks are very busy this year given the exchange rate. There are more Americans coming to Canada and us Canadians are staying here!
