Canada also produced a few sovereigns, reigns of Edward and early George. They do have a fair amount of value because mintage was low.
I have a few lateish King George V, left over from that time when I bought them as gifts. Canadian banks always had some for American tourists and buyers like me, as well as some Imperial Russian gold coins which nobody much wanted at the time. USSR, of course, needed money and was selling off whatever was in the treasury vaults, etc.

Some people buy gold coins as an investment, but bullion and certificates are cheaper. Australia, Canada and Austria put out very attractive gold coins, very popular.
Canada- www.mint.ca
Other countries- www.talismancoins.com; good illustrations.