Ok Toronto to Buffalo is a two hour drive and it depends on traffic. If you go during rush hour, it could take longer. Plus you never know about the weather. It can be really bad when you closer to the Buffalo and Niagara FAlls. If you want to go to the outlets, the prime outlet in Niagara falls is the best and where most people shop when they go across the border. There are a couple of small malls near there, but nothing great.
If you want to hit up a big nice mall, then Walden Galleria is the place to go. However, this will take 20-30 to drive there because it's difficult driving there if you don't know your way from the outlets to there. It's a bit of a distance. But it's worth it.
Target is anywhere and everywhere, so you can hit Target by the outlets and/or by Walden. IT's a lot to do Walden Galleria and the outlet mall on the same day, but it's doable. You have to be really really good with highway driving and with a map. And have loads of change ready for the tolls.
Plus, you have to declare EVERYTHING at the border on the way home and pay all your taxes and duties. No goes through the border without claiming these days.
Mel