That is true given you will need your passport and your COPR to present to CBSA to complete your initial landing. You will get your PR card in the mail only of course if you provide a Canadian address when you land. As per my other reply how long you can drive on a valid US license can vary by province, often only 90 days before you need to exchange for a Canadian one but as far as I am aware not something of any concern to CBSA, more a police matter if you are stopped at some point..