I have never shipped a bike by Greyhound, so I can't help you there. But for the box, you might want to find some bike shops in Jasper and explain to them that you will need your bike boxed for shipping when you arrive in Jasper.
They might be able to handle your request. Some shops might take a couple of days to box it, others will do it right away. I know that the shop I work with will do it right away if you set it up prior to getting there. We also save boxes for people that want to do it themselves. Either way, if you find a shop that will do it, I would email them again a day or two before you arrive to remind them.