The hubby and I rode part of the kettle valley railway, it's quite scenic and easy pedaling for the most of it. We took our hybrids and took our time. Parts of the trail can get quite busy on weekends and holidays etc.

As far as cycling parts of Alaska to Jasper this late in the year......
You might want to reconsider, I don't think it would be all that pleasant of a route to be cycling. Your going to run into all kinds of not so nice weather. Plus it's getting dark around 730pm now, and the temp is dropping once the sun goes down. Our rainy season will start soon enough, that would be something else to consider. If you happen to go, pack warm waterproof clothes.