Whether you sell to Canada or the USA, you do pay fees to eBay and to Paypal.
EBay gives you your first 50 listings free, any after that cost 35cents each. This fee is charged every time you list.
Auctions last seven days* and then close. Fixed Price listings last 30 days and will then automatically renew.
If your listing sells, you pay eBay 10% of the selling price.
If you charge shipping**, you pay eBay 10% of the shipping fee.
Paypal will charge you 30 cents PLUS 2.9%*** of your customer's payment for processing.
Your customer's payment will be held for up to 21 days against your service, so mark your item shipped immediately. Add tracking if you used it.
You can buy discounted postage through Paypal, and can use those Held funds to buy it. You also get a discount on some services.
Use the link I gave you to sign up for Canada Post's Small Business Solutions service, which gives you those discounts.
*There are other auction lengths. Ignore them.
** And bookmark this: https://www.canadapost.ca/cpotools/apps/far/business/findARate?execution=e1s3
*** As dennis says, more for non-Canadian accounts.