From the eBay order page, click the Canada Post tracking number and look at it on the actual Canada Post website. The tracking might be incorrect on eBay. Look to see what it says directly on the Canada Post website.
Since this likely isn't an expensive order, I would wait a day or two before doing anything, just to see if it shows up. It is possible that it was dropped at the wrong house. If the person leaves it for Canada Post to take back it could end up delivered in a day or two. Packages and letters get delivered to the wrong house by accident sometimes.
Otherwise, I would contact both the seller and Canada Post customer service. The seller isn't responsible to refund you if it is marked as delivered, but if this was shipped Expedited, it was probably insured, and they may be able to open a claim. Or if it was misdelivered, it might get returned to sender, etc.
