The only block that I'm aware of regarding payment on the Paypal site is to block non U.S. Paypal account holders which obviously, you don't want to do. Even if you could block a buyer from a specific country from using Paypal you might be blocking someone who has a foreign Paypal account and a North American address.Also, unless you have a shipping cost listed for their location, the buyer can't pay.
In you eBay site preferences you can check off under Buyer Requirements Block buyers who "Have a primary shipping address in a location I don't ship to"