The problem is the 2 different conflicting laws. On the one hand, the SAAQ allows you to modify the exhaust as long as it's not louder than the original and that it passes mechanical inspection (meaning it works and has no leaks or flaws, regardless of sound, shape or size), whereas the "CSR" states it must have the same characteristics as the original if changed.The problem is how vague the word "characteristic" is. If it's an inch longer, it's not the same, if it's a different color, it's not the same, if the tip is on a different angle, it's not the same. So basically, if they want to, they can give you a ticket for any muffler that was not installed when the car was built in the first place.
Now, the 2013 question being if the car had the possibility of being delivered from the manufacturer with said "illegal" item, but it wasn't and it ended up being installed by the dealer, then technically, no it's not legal. However, if said part carries the manufacturers logo and it WAS installed by the dealer, the court may let it slide. This will especially be true when the vehicle in question is older and has no reference to what consists of "original." For example, an R32 Skyline GTR has a stock free-flow muffler, but rare are the ones still with the stock line. So a Nismo after-market line would be acceptable since there is no reference.
In any case, the best thing to do is not get an overly easy-to-spot exhaust and to drive quietly and responsibly in the streets to not get bothered.