I know that Disney Gift Cards that are purchased at a Canadian Disney Store are accepted as a form of payment on the Disney ships, so I would assume the same goes for Disney Gift Cards purchased with your credit card points (what a great way to save on a Disney vacation!). When using the gift cards, the Canadian amount (based on the current market value/exchange rate) will be converted into a US dollar amount.
When you check in at the port, each guest in your traveling party will be issued a Key to the World Card. Your Key to the World will act as your boarding pass, stateroom key, and be used for all onboard purchases, as Disney Cruise Line uses a cashless system. You'll be asked to provide a valid credit card and any charges made during your sailing will be added to your stateroom folio. If you'd like to apply Disney Gift Cards to your stateroom balance, you'll simply need to stop by the Guest Services Desk in the lobby. The gift cards you've applied to your account can be used to take care of these onboard expenses.
I hope this helps with your planning (and budgeting!) for your upcoming Disney Cruise Line vacation. Have a magical day! - Diane W.