Almost every store has something on sale on Boxing Day. Even Wal Mart has joined. It depends on what you want to buy. for electronics, Future Shop is the first choice. For office article, Staple is quite good. and so on. see the flyers and newspapers before Boxing Day.
you can check the ad on the newspaper before the Boxing day, and even try order on line to avoid the traffic. we usually go to St Laurant shopping mall, they have the bay, sears and other good stores. future shop is not far away