Parks Canada has continued to maintain an excellent network of trails and campsites. Some of these campsites can get busy (any campsite near a town definitely will be). But the bulk of backcountry campsites are empty to half empty for most of the hiking season. If you're planning on staying somewhere popular (anywhere near the town of Banff) or camping in July you should reserve a site with Parks Canada.
'''Fees'''
Seasonal camping passes are available from Parks Canada. This pass entitles you to use any Parks Canada campsite in all the mountain parks for the duration of the season and usually costs 40-60 dollars Canadian.
'''Season''' By late June most passes will be clear enough to be negotiable. By the end of September most passes have accumulated a bit of snow. By early October long distance hikers need to be extra mindful of bad weather.
Weather in the Rockies is chaotic at any time of year. A warm sunny day can turn into a subzero blizzard overnight only to be a blazingly bright and warm by morning. If conditions deteroriate swallow your pride and head for lower ground regardless.