You have 30 days from delivery to open an Item Not As Described Dispute in the Resolution Centre at the bottom of this page.
The first suggestion is to Contact the Seller.
Don't get hung up on this point.
Don't accept an offer of a replacement.
You want a refund.
If the seller does not send a refund promptly, ask eBay to step in and escalate to a Claim.
The seller is required to send you Return Postage.
If the seller is not in Canada, he should send the money by the Send Money service of Paypal and state that it is for return postage.
It will help him if you can tell him the correct amount you will need.
https://www.canadapost.ca/cpotools/apps/far/business/findARate?execution=e1s1
You will be refunded when the package shows as Delivered to him. Keep an eye on this.
If he does not send the return postage, you will be refunded.
He will also get a Defect.
Defects are killers to seller accounts.