OOPs..I see you're comming across the rainbow bridge.
There is a bike path which parralels the niagara river but only to the north Grand island Bridge.
From that point you have to take Buffalo Ave to Military to River Road whcih will take you into North Tonawanda/Tonawanda (the bike path is in Tonawanda).
I'm going to put you in touch (send you the e-mail addy) with someone from Niagara Frontier Bicycle Club as The City of Niagara falls NY is like Beruit with all the potholes and torn up streets and were it me, I'd definitely want to get on to the upper mountain road (gorgeous scenery, way less traffic, slight downhill all the way)which is a direct route right into Lockport.
The bike path-Buffalo ave-River Road-bike path is a good 17 miles worth of uninspiring riding (unless Love Canal is your thing)added on to your already long trip.