For the hell of it, i added a random vacation just to see the checkout and it shows Air Canada gift card is an payment option
Pay with Air Canada Gift Card
Option 1) You can use up to two (2) gift cards to pay the total cost of your booking.
Option 2) You can use a credit card to pay a portion of your balance and a gift card to pay the remaining balance. First enter your credit card information, then enter your gift card information by clicking on "I would like to use more than one payment card" located below your billing information. Indicate the amount you want to pay by Gift Card, and the remaining balance will automatically be re-calculated in the credit card section.