To me...and I don't know anything about Canadian laws...it would seem to me, that if his only proof is, it sounds loud, that you should be able to fight this in court.
Unfortunately, the cop sounds like a douchebag that will just make up something everytime he sees you.
2011 E92 M3
| Melbourne Red | Black Novillo w/Carbon Leather Trim | M-DCT | Competition Package | Premium Package 2 | Convenience Package | Enhanced Premium Sound | Heated Front Seats
2004 E46 M3
| Silver Grey | - Retired