You can get by without a car in downtown Niagara Falls and Stratford if you book a hotel close to the action.
Avoid Toronto-area highways during weekday rush hours (6:30 to 9:30 am and 3:30 to 6:30 pm). Traffic between Toronto and Hamilton might crawl along at any hour.
Ontario's only toll road is the east–west Highway 407, north of Toronto. It's expensive (22¢–25¢ per kilometer) and has no tollbooths; you will be billed via mail if the system has your state's license plate information on file.
The Ministry of Transportation has updates for roadwork and winter road conditions.
Ministry of Transportation (416/235–4686 or 800/268–4686. www.mto.gov.on.ca.)