Niagara Falls is definitely a place I would go back to. It's around 150km from Toronto. You can either book up an escorted day tour which includes the boat trip and the journey behind the falls. It also includes lunch and then a visit to a winery on the way back. I recommend pre-booking and I can do that for you.
Another choice simply spend a night or two at Niagara and do the trip yourself. There are various hotels overlooking the Falls and one of the best has to be the Sheraton hotel and I would opt to stay in one of the rooms with a Falls view. The prices are not expensive.
Niagara falls is between the U.S and Canada and you can visit both sides by just crossing the bridge. However if you are visiting from the Canadian side then there really is no need to cross the bridge as I think the Canadian side has the best views.
The day tours from Toronto are around 150 dollars per person. If you take the Greyhound coach from the coach station in Toronto the price is 40 dollars per person return. The journey takes around 1 hour 30 mins and the coaches are frequent and all have wifi on board.
Once arriving into Niagara, the Falls are 5 mins by taxi or you can walk all the way along the river which takes around 30 mins. I really recommend this, the walk really was amazing.
Niagara Falls has three waterfalls, two combined and then the main one which is the horse shoe shape. They are very close together and if you take the boat trip which is 20 dollars per person you will go right next to the falls. So close that they give you ponchos because you get wet from the spray. The roar is absolutely amazing and you can literally take hundreds of pictures like we did.
You can also do the journey behind the falls which we didn't actually do but it's a walking tour and you will learn some more history,
I really recommend staying 1 night here and make sure it's a Wednesday or a Friday as they have a spectacular fireworks display over the falls. The boat trip on those nights is an hour and it's 30 dollars per person but it is supposed to be amazing. The boat trip during the day is around 30 mins.
There are plenty of restaurants and bars in the area also as well as the Hard Rock Cafe.
Please ask me if you need to know anything else.