are there companies out there that insure expensive jewellry sold on ebay.ca
Yes.
If you are in business,selling a lot of high value stuff, try HughWood International which specializes in collectibles.
They have a Torontooffice and cover in transit, trade shows and flea markets, collections, and dealer stocks at a better price than the less specialized firms.
I don't deal with any one-off insurers so I hope others will jump in. You may have to post a new question.
Of course, you will win a Not Delivered Claim if you use Signature Confirmation.
