Are you using the horrible Simplified Sell Your Item form?
You can change that to the much better Advanced/Business SYI form from a link at the top left of the bad one.
Are you enrolled in the new Managed Payments program or still with Paypal? Managed Payments doesn't allow for the sale of coins or bullion (yet, eBay is saying "Real Soon Now".)
The URL should say ebay.ca for Canada right at the top of the page.
I've had problems with the site switching from one ID to another when I change sites, and it is annoying. But not changing sites.
You can include Canada in shipping if you are on the USA site, just as you can include USA in shipping if you are on the Canada site, but that is not your problem.