Sleep Jasper
While there's nowhere near as much accommodation here as in Banff, the town of Jasper has a pretty similar selection. The main difference is that there are fewer motels and cabins are a more popular option, but there's also a choice of hostels, plenty of private rooms on airbnb and a selection of giant front-country campgrounds.
Overflow camping
Even so a peak times it's hard to get a last-minute site at many of the campgrounds, so it's good to know there are plentiful last-minute options about a 30min drive west of town at the Snaring River Overflow Campground.