My wife and I rode up to Banff from northern Idaho a few years ago. You only need a night there, then ride up to Jasper on the Icefield Parkway (around 175 miles).....it's really incredible! Stay at Jasper. Since you'll be coming this far, you shouldn't miss it! The town is a tiny version of Banff, not so touristy.
On the way back we stayed the night at Radium Hot springs and visited the hot springs there. It's a very nice and large facility. Or, on your return trip, take highway 40 as sonarman suggested and route yourself down to Waterton National Park and Glacier National Park. You've got to ride the "Going to the Sun highway." Please read my trip report below for more info....Selkirk Loop & the Canadian Rockies. It doesn't include Glacier, but we've been there and it's definitely worth riding. Don't miss the side trip to Many Glacier (turn at Babb)
Have great ride !