81km/h in 50km/h zone

I just got pulled over for 81km/h in 50km/h zone in mississauga close to eglington and central pkwy. I had just made a left on from Eglington on to central where the speed limit changed and I did slow down probably before the 50km/h sign but the cop probably had it radar on before then. What can I request in the disclosure that will help me that he clocked me before the speed sign. Anyway he reduced it to 65 in 50km/h with the usual comment that he will charge at full 81km/h if I go to court. I am assuming that if I pick the trial option and can't figure out that he clocked before the sign from disclosure, I can still plead guilty in front of judge or persecutor and end up up the same amount $57.50. I had one minor ticket for which 3 years end this september and my renew is march 10 so by next renewal I would be back to one minor ticket assuming it is considered a minor and my insurance johnsons allows one minor. What should I do?They can't reduce it further unless cop does not show up which I can't tell or not much else is going for me here towards fighting it. What should I do?.

Not sure that would work. No sign = 50 km/h in Mississauga.

I guess just have the take officer's word, because I didn't realize I was doing 81km/h