I don't doubt it will remove some vehicular traffic, which is great, but once you get to Canmore of Banff and want to venture out and explore then what? Transit and shuttles will only take you so far.
Also, depending on why you're going to Banff and what gear you have with you, it may still be more practical for you to take a vehicle anyways. This will especially be a consideration for domestic tourists (such as myself) who bike, hike, ski ect... there frequently.
International tourism to both places will be much easier and more attractive, especially if this is directly connected to YYC. "Tokyo/Beijing to Banff via Calgary, take the train from the airport and get there in 45 mins!" will certainly be promoted to the max. With more people mingling about, both places will struggle to keep up with the increased demand (especially Banff), and thus prices will go up.
I'm good with Jasper