Amazon.ca chase visa is the best visa in terms of no foreign transaction fees. Most banks in Canada charge 2.5% on foreign currency transaction. For example, if you use your Canadian credit card in US you will be charged 2.5% of the transaction amount.
Amazon.ca visa doesn't have that and it has no annual fee.
It is good to have a USD account in a Canadian bank however, banks do not always give good exchange rate. I have worked at a big five bank in Canada so I know from experience. Best is to use a credit card such as amazon visa and Visa has one of the most competitive exchange rates. Better than Canadian banks for sure!
Also, USD and other non CAD funds are no CDIC insured. (Canada Deposit Insurance Corporation guarantees up to 100 k in CAD funds in checking, savings accounts)