I imagine you were looking to use a free J class upgrade coupon.
This J class upgrade scheme is just a well orchestrated plan to get you hooked on J class and then desire it so much that you are actually willing to pay the full price some day.
I believe your upgrade coupon is space available and that Air Canada has a contractual obligation to put deadheading staff in J class ahead of you.
Everything in the employees’ contract is there for a reason. The deadheading employee upgrade should not be assumed to be a “perk”. It is probably really a “let” as many other airlines deadhead their employees in J as confirmed passengers.
Having well rested, contented, flight and cabin crew can actually improve the overall travel experience of the paying passengers. And as a result, contribute to the bottom line of the airline.
Unfortunately Air Canada management has still not figured this out.
They seem to prefer the practice of management by confrontation.