You pretty much have to check for Canada Parks daily until you find something. We went to Banff last July and didn't really have trouble finding a campsite open. We booked for Two Jack Main (no hookups) in Banff last March. The longest dates we could find was a 3 night stay. Bathrooms, showers, dish-washing stations are in each group of sites. Firewood is free.
BTW, Two Jack Main was not on the Garmin GPS.
Richard & Jill
2014 Flagstaff 832IKBS Classic Super Lite
2018 Silverado 1500 Crew Cab Z71 4WD All Star Edition
Camping since 1989, seasonal since 2000
Car Shredder Op/Tech, Scrap Metal Recycling - retired
The Faster I Go, The Behinder I Get.