If the immigration officer offers you to renounce your PR on the spot, you should make sure that they give you a visit visa instead so you can continue with your visit. You will not be a PR any more in that case and you will not have health care in Canada, you can not work in Canada etc.
However, if you are just about to visit, you might as well keep your PR for now. If you and your wife decide that the best option is to renounce your PR and have her sponsor you, you can renounce it and she can apply to do that and hopefully it'll be through before too long. You can see the processing time for spousal sponsorship here: http://www.cic.gc.ca/english/information/times/perm/fc-spouses.asp