You'll be able to get a bike box in Jasper - just give yourself an extra day to find one and ship your bike. Greyhound may not put your bike on the same bus as you so you should ship it one day earlier than you plan to take the bus yourself. Also note Greyhound will charge you to ship the bike as well as for your ticket so it can get expensive. I looked at taking Greyhound from Calgary, Alberta to Jasper with my bike and then ride home. It was very pricey and I would have had to go to the bus station twice - once to ship my bike and then again to take it the next day what a pain!
I ended up convincing my boss to drive me the 5hrs there and then drive home alone...lol...that was less hassle than Greyhound!