Kitco is good, been around for a while. I've heard of the bad gold cloning, but not from Canadian mints. I think the Canadian gold is fine, but like it was mentioned, you can always get it tested (I've bought the Canadian gold coin and Euro 100 gram). You can get the new Olympic gold coin that just came out. When I pick it up, the Euro gold sometimes comes with a certificate.
Here's the site:
https://online.kitco.com/bullion/completelist.html