So what is the correct procedure if you have booked a non-refundable AC ticket through Expedia (.ca, forTD, etc.) and you need to cancel it, but would like to use any remaining funds for a later booking?

Expedia has a "cancel" button their website. Can one cancel there and then use the remainings funds for a new booking on aircanada.com? Or does one have to call Expedia to have the remaining funds available? Or...?

TNX