My husband and I took the train to Jasper and rode back to Vancouver in May 2014. The most scenic and memorable sections were the back road portions: Little Fort (south of Clearwater) to 70 mile on Highway 24 through lovely ranch country, and from Clinton over the Pavilion Range to Pavilion. This road is unpaved after Downing Lake, and it runs across the Diamond S Ranch. 950 km in 10 cycling days and one rest day.
How much time do you have? Perhaps you could ride from Calgary to Banff, then Jasper, then our route from there?
P.S. More bike touring ideas here