Here you can check out exactly when thanksgivingn is in 2013. See important dates below.
According to traditions in the United States the first Thanksgivig day was celebrated in 1621 on the deck of Mayflower. The settlers got help from an indian tribe who tought them how to fish and hunt on that country. The story says that 51 settler stayed alive, and their leader, William Bradford organized a huge fest where the indians were also invited.
The canadian traditions says that the origin of Thanksgiving day was a Feast organized by Martin Forbisher in 1578. Probably some americans brought the tradition to Canada when they were escaping from the war of independence.