Ugh, Every seller's nightmare.
Nobody ever ends up happy.
Contact the seller (if you have not already).
She should be paying for the return shipping.
Problem.
If she is not in Canada, she can't send you a return label.
She pretty well has to send you the cost of shipping (with Confirmation of Delivery). You can let her know what that will be. Here is the information.
https://www.canadapost.ca/cpotools/apps/far/business/findARate?execution=e1s1
When she sends you the money, you return it TO THE SELLER.
Once upon a time I would have said, send it to the other buyer, but you don't know who that is and she has your "more expensive' purchase.
So it goes back to the seller.
Meanwhile if all goes well, the other guy has also returned your item to the seller. (Keep all your fingers and toes crossed on that one.)
When the seller has your purchase back she can resend it, you leave postive feedback and all is well.
If the other buyer is difficult, or if there is any other delay, go to eBay for an Item Not As Described dispute and get your money back.
Keep it polite and friendly as much as possible.
I am sympathetic to the seller who will be out the return shipping on the misdirected packages plus the new shipping to the correct buyers, but it was her error and she should put on her big girl panties and deal.
She's going to lose money on this, but that is her problem not yours.
Money or your item.
You should not be paying return shipping out of your own pocket.
And in the long run, it will probably be money you get back not the item. Sorry.
