I am shortly travelling to Canada to do an RV trip with my wife. The middle itinerary looks like:

Day 5 - Arrive in Jasper & stay in Waipiti Campsite for 2 nights
Day 7 - Move to A Campsite in Rampart Creek
Day 8 - Move to Lake Louise Campsite for 2 nights

I've read a lot both here on the official parks website and on multiple other websites that I need to buy a pass. I have no problem with that.

What I'm confused about is when I actually buy the pass, and whether I need multiple for the different stays. I have already booked my campsites in the three locations due to the size of the RV.

So My Question Is: How & When Do I buy passes for the Canadian national parks?