We were in Jasper last week and Banff the week before. Whistler campground in Jasper has over 700 sites but, only about 80 with full hookups. I think it is the only one in the park with hookups. As others have said Tunnel Mountain in Banff is the place. It also has about 80 or so sights with full hookups.
For reservations
http://www.pccamping.ca/parkscanada/