Try KIAG Niagara Falls International 

BTW make sure you see the Maid of the Mist boat going round at the bottom of the American Falls and the elevators going up and down on the tower on the Canadian side.

It's almost more or less mandatory to fly whatever it is you're in (preferably something like a 747 at the minimum or an Antonov with Space Shuttle) inverted under the bridge near the platform you stand on in real life to see the falls just below the American Falls.

If you don't believe me ask Ozzy......