You can find the duty rate - if any - on the CRA website - often it depends not only on the item but also the country of origin (where manufactured). You should also check with Canon whether they will honour their warranty in Canada for a printer bought in the USA. They do for lenses and cameras, but I don't know the policy for printers. Also it is advisable to find-out who takes shipping damage risk - the store, the shipper or you? (It's a big heavy monster.) The fact this printer is being so heavily discounted relative to its launch price is something to think about.
Printers face no duty like most electronics (spoke to CBSA today). You would pay GST, PST, and any fees from the shipping company for brokerage fees, etc.
Still, with the weak US dollar, it might still be better to go with a US supplier.