OK I just finished the Assassin's Creed trial and got sent to the PSN Store to buy it (which I didn't). At first I just went to buy it to see how much it would be with tax (as I usually have to pay tax on PSN purchases) and it said no tax. At first I thought this was just for full games, but I looked at a lot of other stuff (DLC, normal games, etc.) and it seems that THEY have no tax too!
So if you live in Canada...no more tax!