Boxing Day is the day after Christmas, though, so it wouldn't be a big 'holiday spending' day. (Maybe holiday returning day, for that too-large puce sweater that your aunt always sends.) Traditionally it was when you gave presents to those service people that you interacted with regularly during the year, like your postman, maid, or the grocery store clerk.
Black Friday is more of a retail invention than anything else, based in the days when people wouldn't even think of Christmas until after Thanksgiving. These days, you see Christmas stuff in the stores as soon as the Halloween stuff is clearanced - if not sooner!
I don't know - do Canadians do a big shopping day after their Thanksgiving in October?