Postal shipping is the best assuming they'll take it, there's a size limit I think. UPS ass-reams the receiver with taxes (6% federal and maybe provincial as well) and something like $40.00 CAD for "brokerage". Fedex is pretty much the same.
Canada Post will charge the 6% tax and maybe a dollar or two handling fee... big difference. If you insure the package (good idea) you should put a reasonable value on it.
You should attach an envelope to the outside labelled "customs invoice" and enclose something with the description (used motorcycle parts), the price, and the country of origin (Japan).