On foot
You can really do a lot without a car once you get to the immediate vicinity of the Falls. If you are staying downtown you may be able to get by without a car. The toll for walking the Rainbow Bridge westbound to Canada is 50¢ both U.S. and Canadian currency accepted, paid on the Canadian side coming into the U.S. There is no eastbound toll. If you travel with any baby carriage, you pay no extra toll. Do not photograph or film on the Bridge without getting Bridge Commission approval and signing a liability wavier first. You cannot walk across the Lewiston-Queenston Bridge. (http://niagarafallsbridges.com)
By bus
NFTA bus #210 travels a little around the Falls area. Other bus routes run in the area, for example to Buffalo.
By bike
Bicycling can be faster than walking to get around. The toll for bicycling and walking the bridge across the national border is the same. On the bridge sidewalk, bicyclists are officially supposed to walk their bikes, but you may bicycle on the far right lane of the Rainbow Bridge and Lewiston-Queenston Bridge like a car.