Jurjen said:
How are rented cars classified? And what about if I take the bus to the nearest town, I walk across the border and find a bus at the next town? What about a car borrowed from a friend/family member if he/she asked me to pay for the gas plus a bit extra (for writing it off), is that commercial?
OK... You can cross the border with your car, friend's car or rental car, you wont have any problem coming back without your PR card because your name will come out in the systema as a permanent resident.
I also found out why CIC does not recommend using commercial transportation when you dont have yet your PR card... the problem is not getting out of Canada, the problem is when you are coming back, no Airline, train or bus should allow anyone without valid traveling documents, otherwise they get fine by Canada from 3000$ to 5000$ if someone enters Canada without valid documentation. So, my friend recommended (40 years working for CIC) to go to the Canadian Embassy to get a visa or a travel document that will allow the Commercial carrier to let you back into Canada.
Hope this help you...