I have just called Canadian custom, Peace bridge at Niagara Falls. The officer said that you still can enter Canada by land ( private car) by using landing paper and passport. when they ask for PR card, you need to tell them that you just lost it. You can call this no. for confirmation, 905 262 4010. I use the same way for my parents to enter Canada few times because their PR card was not returned by Toronto airport. Good luck!!!