Ontario car rental companies will require you to provide identification in both a driver's license and passport. If you're from the United States or Canada, the rental company may be able to look up the driver's license information. If you're from outside of Canada you will also need to provide your passport. The rental company will take note of the passport number and compare the photos with that of your driver's license.
A current insurance card and contact number of your insurance agent and company must be brought along to Ontario car rental companies. Whomever is renting the car will need to be an insured driver. Insurance can also be purchased from the rental company but either way, the person renting will need to have some form of insurance coverage.
Car rental companies in Ontario will prefer payment in the form of a credit card. Whether you are paying up front for your rental or at the conclusion, paying with a credit card allows the rental company to charge you after the rental has been returned in the event there are any problems. Also, by paying with a credit card that is accepted worldwide, rental companies in Ontario will be assured that they will be receiving payment.