I'm not sure about Canadian traffic law, but in the US (in most states and jurisdictions), the courts have the authority to amend the ticket charge, and the terms of the ticket, meaning that instead of throwing the ticket out on an inaccuracy regarding the posted speed limit, they will simply change the posted limit you violated to the correct one. So since you were still speeding 32 km/h over the limit, that is what they will give you. This is a mere reduction, rather than a dismissal.
If I were you, I would go to court. Again, I'm assuming that Canadian law is similar to US law, but your best defense would probably be to question the credibility of the officer. Since he made a mistake as to what the speed limit really was in that zone, grill him on other technicalities that may diminish the credibility of his speed readings, etc.
Good luck

