If retailers are still promoting the rebate, it may be worth a call to the Canadian (or provincial) version of the Attorney General's office. Intentional or not, it is a deceptive trade practice. If you care about it that much, take some tangible action. If it happened to me, I would be upset too.

More broadly, I don't think this is going to stop the average Joe/Jane American from going to Canada. I'd wager that the vast majority of Americans did not know about the tax rebate in the first place. Of those that did, it would be a precious few who actually took the time to apply for it. I've traveled to Canada many times, but only applied for the rebate once. And a few weeks later I got a check in the mail for something like $23. Whoop-de-doo. I'm sure there are some people who will turn up their noses at Canada because of this, but I just don't see it having a substantive effect.