Yes, the SIN will be dormant and will have to be reactivated but I wouldn't see any problems because of that. Service Canada is not immigration and as far as I know, they have no duty to rat you out to immigration. Because of the privacy act, it is even possible that they are not allowed to share info with immigration.
The difficult thing is getting in without getting reported and after that, surviving for 2 years convincing everybody to accept your old landing papers as proof of your PR as opposed to a PR card. The main thing is getting health care. You can live without a car as long as you make sure to live and work in an area where you can get public transport.