Most U.S. and Canadian insurance policies cover both countries. Insurance laws differ between the two, but your policy most likely includes a provision for travel across the border. When you cross, your policy is still active. However, it’s a good idea to contact your provider to confirm. Your agent may also send you a temporary insurance card to take with you. In addition to this documentation, you should also pack your proof of citizenship.
Traveling to Mexico is different. U.S. insurance companies may provide coverage for vehicle damage in Mexico but not liability coverage; you must purchase a separate policy from a Mexican insurance provider. You may be able to purchase coverage as you cross, but having it in place before you start your trek is preferable.
Do you plan to leave your car at home and travel abroad? If you rent a car in another country, your insurance policy usually doesn’t provide coverage. You will need to purchase rental insurance. The U.S. embassy in that country can provide information about the rental car insurance requirements there. Some places require coverage which is only available in that country.