Not every country has characters, and nobody is guaranteed to be out. That said, here's a list of likely places to find them:
Norway: The Restaurant Akershus has a princess character meal.
China: Mulan and Mushu can sometimes be found at the back of the pavilion, near the open area of the department store where "Wonders of China" lets out.
African Outpost: Occasionally, Timon and Rafiki (and, rarely, Terk) are here.
Germany: You can often find Snow White and Dopey to the left of the Hummel store.
Italy: Pinocchio, Gepetto, and Gideon sometimes make appearances outside the chocolate shop.
Morocco: Aladdin, Jasmine, and the Genie can sometimes be found either in the back of the pavilion near the Restaurant Marrakesh, or down near the World Showcase Lagoon.
France: Belle and (rarely) Beast can be found behind the perfume shop.
The UK: Pooh & Friends hang out in the very back of the shops.
Canada: Koda & Kenai are sometimes out by the old Beaver Tails station, and sometimes closer to Le Cellier (I think Koda keeps hoping someone will give him salmon).
You can also sometimes find characters on the walkway between the International Gateway and the UK. I was there last week, and I saw Chip and Dale.