Okay, so there is actually little reason why they would have a Black Friday, because they don’t celebrate Thanksgiving like we do.
The reason why there's a Black Friday in Canada too now is because Canadians kept going to USA to do their christmas shopping on Black Friday rather than doing it in Canada, which hurt their sales, so they try more and more to lure people on that day. I noticed that every Canadian store that do Black Friday (in my case, about 40% of the local shopping mall) have it last for 3 days.
That said, Canadian Black Friday only exists since 2011, so it's still not that popular yet compared to boxing day. I didn't find anything I needed that interests me for now (most TVs that were on sale nearby are 40-46 inch and I would rather prefer waiting for a good deal on a 55-60 inch or something), but one gift I planned to give to someone was for sale today. There were more people than usual, but I went at around 4 PM so it wasn't as bad as it would have been at 2 PM, plus most people are working today, unlike in USA.
I think in some cities boxing day might look even worse than USA Black Friday Eeems, especially if it occurs on weekends, because of the very restricted business hours. In USA you got people going shopping at 12 AM to get the best deals possible, and you got plenty of people who want to spend the night with their family and shop the day after thanksgiving, then add the people who prefer waking up late and doing it during afternoon or evening. In Quebec, you only have a 4 hours shopping timeframe (sometimes 8 ), so everyone has to go at once.