The best evidence that the Crown has of the 117 in an 80 is the radar reading. If the radar is not tested properly or is not used properly, the radar evidence should be excluded. All of the information regarding proper test/operation is in the manual. Being able to ask the officer exactly what he did to test it and how he used it, and compare it to the manufacturer's procedure, is central to the question of whether or not the radar reading is reliable.
He does have something to lose. Typically Crown's will not take a deal on the day of the trial. They've set aside court time, called officer(s) in (possibly on OT) and prepared for the trial.
What are you basing this on? The Crown offers plea deals on the day of the trial as a matter of routine. The court date is scheduled usually based on the officer's availability. They set these up for rapid processing. Every time I've gone to traffic court (twice for my own purposes, 10+ times as an observer), the Crown tried to plea-bargain with the defendants in speeding cases. The Crown has already paid the money and they don't want to walk away empty-handed.
Not to mention the fine will be higher than if he just paid it.
Not necessarily. Raising the fine to the statutory amount can happen but the JP can lower it, too. Some other provinces, such as Quebec, make you pay an additional surcharge for court time if you fight it, but not here. The max they can impose for a Part 1 offence is $500. The way to argue, upon conviction, for the set fine (or less) is here:
http://www.ticketcombat.com/step5/sentencing.php
That assumes that the Prosecutor successfully gets a conviction. Right now the disclosure is still not complete. If they do get disclosure of the relevant parts of the manual, the game changes.