It's colder up here and the harvest is earlier, but that's not the only reason for the timing.
The second Monday in October is the Canadian Thanksgiving holiday, which is sort of like American Thanksgiving but not nearly as big a deal, and with none of that New England Plymouth Pilgrim backstory. Most Canadians have their big family get-togethers at Christmas, which is a two-day holiday here with Boxing Day tacked on. For Thanksgiving, there are no Black Friday sales (although the stores really try) and for most people, it's pretty low-key.
On MNN last year, I had a look at its history, and why it is so early- a political decision made so that workers wouldn't get too many days off so close together. More in MNN.