The AA exhaust is sold as being completely street legal. Do you have an x-pipe that is for off-street use only? If NOT then what more do you need to prove in court? You brought a product that is legal, your car is road-worthy and you weren't doing anything wrong like speeding. Cops in Canada are extra d*cks. Maybe they're being even harder right now because of the $2 million seize in Van city, every cop thinks they have more power now.
Side-note; are there actually any cops on bimmerpost?!