I’ll chime in with getting the ferry over to the island and do the evening stand up paddle board tour if you so inclined. There is a good little restaurant over there that you can stop at before the tour starts... it’s the green and White House that you’ll walk past.
As far as Niagara is involved, I’d rent a car and split the day at the falls then on the way back at Niagara in the lake. The area around the falls themselves is all a bit tacky.
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