Since 1957, Thanksgiving in Canada (Jour de l'Action de grâce) has been celebrated on the second Monday in October (the same day Americans celebrate Columbus Day). Canada has always celebrated Thanksgiving earlier, but in 1957 the Canadian Parliament declared that the second Monday in October would be recognized as;
“A Day of General Thanksgiving to Almighty God for the bountiful harvest with which Canada has been blessed.’’
Why do the two countries celebrate on different days? There's a couple of reasons really.
You might already have guessed the first reason, it makes logical sense. Canada (for the most part) is further north, and therefore has a shorter growing season, and the harvest has to come in quite a bit earlier than it does in most of the U.S., so therefore it makes sense to celebrate the harvest earlier as well. Much of Canada is already experiencing winter weather right now, and a harvest festival wouldn't be a very cheery occasion at the moment.
The second reason is also pretty obvious (now that I'm going to mention it). Canadian Thanksgiving and American Thanksgiving are not celebrations of the same thing. In general they are pretty similar in that they are both harvest festivals with their origins in Europe, however, specifically, American Thanksgiving, as well as giving thanks for the bountiful harvest is also a commemoration of the 1621 celebration at the Plymouth Plantation. This was a feast shared by the pilgrims and native Americans. Canadians do not commemorate this event.
The first Thanksgiving in Canada occured in 1578 when the explorer Martin Frobisher, after successfully arriving in Baffin Island after a particularly gruelling crossing in search of the elusive North West Passage, held a ceremony in what is now known as Frobisher Bay. He and his crew celebrated communion and gave thanks to God for their safe landing (and I'm certain they prayed very hard to be returned safely to the comforts of Europe). In later years settlers came to this country and brought with them their traditions from their home countries. A harvest festival is a universal custom, and I'm sure that just about every culture celebrates this event. I'm also sure a lot of our traditions have been pinched from American traditions as well.
In any event, everybody on this continent has many reasons to be thankful all year round, so setting one day aside to express this thanks isn't really asking a lot.
Happy Thanksgiving 2011.