I did a bit of research and found out that Montreal had some of the largest horse slaughterhouses in the world. Apparently there are plenty of places in the world like Texas or Saudi Arabia with a lot of horses, and laws against slaughtering them for meat.
However if you're breeding a lot of horses you're going to end up with non-performing animals or too many horses for the space you have. So what can they do? They ship the live (healthy and not sick) animals to Montreal. They're slaughtered there and then shipped to places where they eat said meat.
Unfortunately they wouldn't let me get a tour, which was probably for the better anyway.