As mentioned in other responses, once you take the oath, your PR card will no longer be valid as you will be asked to cut it infront of the officer so you wont be able to enter canada unless you have the canadian passport.
I have to ask if this is real thing that can not enter to Canada without the canadian passport after the oath and gettingthe citizenship? Is there something I have missed..because I have never needed a Canadian passport (or pr or visa either) when I have came to Canada. My current passport works just fine when traveling?