Here is the info on the Air Canada website:

Refund Services

If you haven't travelled yet
Always present your refund request via your original point of purchase.

If you booked at aircanada.com, you can cancel your booking online by going to My Bookings.

If yours is a fully refundable fare, this will automatically initiate your refund process.

If you booked directly with Air Canada, or you're cancelling a booking for which an upgrade was confirmed, contact Air Canada Reservations.

If you booked through a travel agency, another airline or website, contact them directly.

https://www.aircanada.com/ca/en/aco/...-services.html


Also on a separate page

Cancel an Online Booking

Do I get a refund if I cancel my booking within 24 hours of purchase?

If you cancel your booking within 24 hours of purchase, we will:

- refund the price of your ticket and send you a confirmation email, or
- cancel the payment transaction (no email is sent in this case).

If you're cancelling a booking for which an upgrade has been confirmed, you'll need to call Air Canada Reservations to request your refund.

Exception: In the case of Flight Pass bookings, credits that are cancelled within 2 hours of booking will be credited back to your Flight Pass account and no cancellation fee will apply.

https://www.aircanada.com/ca/en/aco/...l-booking.html