From the Greyhound Canada Website:
5. Bicycles in Baggage Service: Bicycles checked into baggage must be boxed. Bicycle boxes are available from Greyhound Courier Express at selected terminals for $10 each (plus GST). You will be charged the oversize charge of $30 plus GST.
Bicycles are carried unboxed on the following routes, subject to space, and no "Travel With" charge is applied:
i) Vancouver - Whistler ($10 charge)
ii) Vancouver - Squamish/Garibaldi ($5 charge)
See:
http://www.greyhound.ca/en/travel_in.../baggage.shtml
I wouldn't count on Greyhound always having boxes available to purchase. They say that your bike will travel with you on the same bus, but this must be a new policy because they didn't always do this in the past.