If your planning a trip at this time of year May - September then it's a perfect time.
If you are flying into Buffalo you could rent a car there and just go across the peace bridge into Niagara Falls Canada. It is only a 45 min drive from Buffalo airport. There are a lot of things to do in Niagara Falls. At the falls there is Maid of the Mist, tunnels that go directly under the falls and a platform you can stand out on that you can look up at the water coming down. If you stay until night time you will will see the falls light up with colours. There are museums, Brock monument, flower clock, tons of restaurants, 2 towers, casinos, hotels, motels, bed and breakfasts, shops and so much more.
Toronto is about 1 1/2 hours from Niagara Falls. There you have the Canada's Wonderland, CNE, CN Tower, Toronto island, restaurants and hotels galore. I only live a half hour from Toronto and I do not know much about it because I do not like it there. Way way too many one way streets and people. lol