For a whole bunch of reasons, it makes sense for sales to be coordinated between different countries, especially neighbors. It allows marketing dollars to be used more efficiently, the logistics of shipping and warehousing are simplified, etc.

Besides, Black Friday is more about kicking off the Christmas buying season than celebrating Thanksgiving. It starts the very day after the preceding major holiday (and when many Americans have the day off). Unless Canadians would be done with their Christmas shopping by now, it would not make sense to tie to Canadian Thanksgiving.