In some provinces it may be against the law to have more than one license and it is certainly not well liked by the police. In majority of cases, you are required to give up your existing license when you get a new license in Canada. I have heard a couple of people say they were allowed to keep their foreign license. I do not know if it is against the law in ON.
If you were to enter the graduated drivers licensing program as a new driver and not mention the fact that you have a US license, you would be able to keep it as they wouldn't know about it. However, if they police ever catch you with both, they will probably confiscate one of them.
You do not need to be a PR to get a Canadian drivers license.
