That's not how it works.
The seller invoices you THROUGH EBAY with both the selling price and the full shipping cost.
This is the only payment you make to him. Best is to do this through Paypal and to back your PP account with a credit card.*
When the item arrives in Canada, if the purchase price (not including shipping cost) is less than $20, that's the end of it.
If the value is over $20, the courier will broker the import. They will charge a fee of $20 or more** plus applicable sales taxes, and sometimes applicable duty***
His way is not "eBay legal". If he is a newbie, tell him that he should pay the shipper from the money you send him for his eBay invoice. No CODs
If he has experience, he is scamming you.
As a side note, does FedEx even operate in China? I've only heard of DHL.
*Because if things go pear-shaped, you can dispute both through PP and if necessary through the credit card.
** If the seller had used the postal system, this charge would only be $9.95.
*** If you want to learn the customs charge on a given type of item, check the CBSA website.
