I have seen the country-themed ear hats for sale at non-Epcot locations including the World of Disney Store at Downtown Disney and at Le Chapeau on Main Street in the Magic Kingdom. I will, however, tell you that the merchandise mix at the Disney shops changes with great regularity.
Your best bet to find out where you can buy the Canada ear hat is to contact the Disney merchandise department directly. You can contact the Disney Merchandise Department at 407-363-6200 or wdw.mail.order@disneyworld.com. They should be able to tell you where in the parks and resorts the hat you're looking for will be sold at the time of your visit.
And as you noted, the Canada mouse ear hat is available through the Disney Store online.