Dare I say it here but car rental is an option for a hassle free trip to Niagara...let me explain a bit
Myself and my wife did a Toronto add on to a Cunard transatlantic crossing in August 2019. After a few days in New York, we took the Maple Leaf from Penn station to Aldershot (Ontario, not Hampshire!), as I had chosen a nice hotel away from the centre of Toronto, at Burlington Ontario.
I chose Burlington as it was (a) a cheaper hotel compared to central Toronto) and (b) because it is 'on the way' towards Niagara. In order not to be restricted to public transport and to be able to see some countryside 'on a whim' we hired a car in Burlington and dropped it off at YYZ immediately before flying home to LHR.
One of the days we had the car we drove to Niagara. (on another day we drove to Mount Nemo park). The car proved the ideal way to get to Niagara with no hassle and on our 'own schedule'. It also allowed us to see the rest of the Niagara area 'on spec'
Our route that day was as follows - it was one of may favourite tourists days in 60 years or world travelling):
Burlington - Queen Elizabeth Way - Glendale - 405 - Queenston Heights Park (large car park with loads of space) - walk to Floral Clock which is the northern terminus of Niagara Falls Canada bus route which runs all the way down the river to the falls. We walked or used the bus all day before returning to Queenston, then driving along the river to Niagara on the lake, Mississauga point (view across the lake to Toronto including curvature of the earth!) - 87 to Lakeport and back on Queen Elizabeth Way.
As an aside, as members of the RHS we were pleased to find that Burlington was a stones throw away from Canada's RHS main HQ in Hamilton. The difference between Wisley and Hamilton is that at Wisley there is no garden through which run triple headed GEs on heavy freight!