I'd simply attend on your first Court date and enter a plea of not guilty while you consider how you want to proceed. Speak with the Crown, and see if they're willing to offer you a plea deal to a lesser offence. In my experience many Crowns will drop the stunt driving charge if you agree to plead guilty to the speeding offence. You'll also want to request disclosure, so that the Crown can provide you with a copy of all the evidence. You'll want to review the evidence and determine if the Crown can sufficiently prove it's case. I'd also suggest seeking the services of a paralegal due to the serious nature of your charges. Unfortunately any speeding conviction at 50+ will likely have serious insurance implications. It's unlikely you'll be given any additional suspension, unless you're a G2 driver since any 4 point conviction (like the speeding) can result in an automatic suspension.
And FYI, the officer can't speak to the Justice of the Peace and request a lesser charge. Only the Crown can offer you a reduced charge, the JP can only determine guilty.
First, hire a reputable Paralegal. This is a serious charge with big implications on both your license status and your insurance. You need someone who knows what they are doing. Ensure they are licensed with the Law Society of Upper Canada because there are a lot of horrible advocates out there claiming to be Paralegals.
Second, I am not sure what that other guy who posted a comment is talking about, but the police can't reduce the charge once it has been issued, the Crown makes the decision with regard to how they want to prosecute. The Justice of the Peace is simply the decision maker (guilty or not guilty). Most often they (the Crown) will offer you a a deal that includes pleading guilty to a "lesser and included offence". Never listen to police who say they will talk to the JP or the Crown, it won't make a difference. The truth is most police know very little about the law (believe it or not). They know how to lay a charge but have no idea how the court system works, that's why many screw up and charges get tossed. Don't forget, there are many cops who have nothing more than a high school education.
Do some research, hire a good representative and order your disclosure as soon as possible. Perhaps you'll get lucky and the cop will have messed up on the testing of the radar gun....If it wasn't done exactely as per manufacturer's instructions it will be tossed.