Yes, so long as you only travelling outside of Ontario temporarily. For example, if you are visiting another Canadian province on a family vacation, your Ontario car insurance should be sufficient. However, if you move provinces, you will need to notify your insurance company and update your coverage. At a minimum, you will need to inform them of your change in address, which is likely to impact your rates.
Depending on the minimum coverage requirements in the province you are moving to and the coverage currently included in your policy, you may also need to adjust your coverage. In some cases, if the insurance company you are currently with does not offer insurance in your new province of residence, you will need to cancel your policy altogether and purchase a new one.