You can shoot NR on Crown or private land without a licence. You should not get into trouble if you can demonstrate that you are out target shooting and not hunting. I would give the local MNR and police office a heads up (if you are shooting at a sand or gravel pit, I don't think it's necessary). Also, make sure you have nothing that can be associated with hunting on you or in your car. A copy of the regs or better yet, a letter or even an E-mail from the local MNR office confirming that you can shoot would be great.
It is legal to shoot without having a licence in Ontario, but, like in every other walk of life, CO's and police do have their share of zealots and adzeholes.You could run into one that knows nothing about the fine points of the hunting regs or who believes that people should not be out shooting, so it's best to be prepared. The absolute best thing to do would be to have a licence. It would prevent any potential problems, but if you run into an adzehole, he or she will find a way to aggravate you regardless.