Your own, personal Canadian Car insurance is valid in the United States when you travel for visitation, but not as a permanent resident of America.
If you have rented a car in Canada you need to check with the specific company and policy you’ve purchased. Always check first, don’t guess and find out after the fact you have no coverage. Different companies have different policies and different exclusions (age of driver, named drivers, geographic limits, etc.). If you are driving contrary to the policy you will ben denied any coverage in an accident, and in America that’s a bad bad thing.
If you rent your car with your credit card, you may have coverage through the credit card company. It’s best to find that out before you rent, and before you decline other coverages. Your own car insurance policy may also cover you while you rent a car and drive in America, but again, find out before you travel about that.
There are huge differences in American and Canadian insurance policies. Statutory minimum policy limits vary widely. Most Ontario policies have $1 million (CND) third party liability coverage. In the US some states have coverage as low as $10,000 (USD). This will have a huge impact on you if you are seriously injured in America. You may be able to claim additional damages from your own insurance company if you are injured, but be prepared that in America payment is usually required upon service provision in a hospital.
if you are in a car accident in America and are hurt consult your car insurer immediately, and with a Canadian Lawyer who will help you find a good American one.
Before you travel to America make sure you have health insurance that will pay for your medical needs – OHIP won’t pay much if any of the costs incurred in an accident in America. There are many companies that sell affordable coverage for short term visits to the USA.
If you are pulled over in America by the police, make sure you are extra vigilant about your behaviour. In America police can be much more cautious, and may be more likely to use force. Keep your hands on the steering wheel once you have pulled over and wait for the officer to attend your car. Don’t begin reaching around the car looking for your licence and insurance/registration before the officer gets to you. The officer may assume you are accessing a weapon.