I’m surprised no one has said london drugs https://www.londondrugs.com/about-london-drugs/about-us.html that is the closest to amazon imo. shoppersdrugmart.ca and fortinos.ca are owned by Loblaws and have an expanded marketplace selection.

Costco.ca is an american company but publicly traded. Well.ca used to be canadian but is now owned by McKesson Corporation which is American and publicly traded.

You could try to buy through etsy or look for canadian shopify stores like bee kinds https://beekindwraps.ca/ ( here is a complete list ) which are more specific sites. You can often find the same products on marketplace sites but the merchant will pay less fees if you go through their own site so try searching products too