I was charged with an improper exhaust , I have had the bike certified with that exhaust and also MTO says that its legal but the cop won't drope the charge, still have to go to court

that is the problem between a obtaining a safety for the vehicle (which ensures that the vehicle is safe for the road) as compared to what is legal for the road

HTA OREG 611 (safety requirement)

The exhaust pipe, muffler and tail pipe shall be complete and securely mounted.

No component of the exhaust system shall be so located as to cause charring or other heat damage to any wiring, fuel line, brake line or combustible material of the motorcycle

HTA 75 - legal requirement

Every motor vehicle or motor assisted bicycle shall be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise and excessive smoke, and no person shall use a muffler cut-out, straight exhaust, gutted muffler, hollywood muffler, by-pass or similar device upon a motor vehicle or motor assisted bicycle

Exhaust charges are often very discretionary, so the officer may still feel that he has grounds to lay the charge, even if the MTO or other officers have said it's ok.