Assuming Canadian law is anything like US law, cases like that can be very hard to prove in court because it's not immediately obvious that the trainer did anything negligent. I've heard of people leaving horses (especially young horses) tied up for increasing lengths of time to teach them patience, so it could be argued that it's a common practice.
Did the colt have a history of not tying well? What was he tied to? Did he have a breakaway halter, or safety tie ring that failed? How much rope was he given while tied? What spooked him?
Unless you have an impartial witness who could answer all those (and more) questions, you're unlikely to get kind of settlement due to the death of the horse.
You might be able to get a refund on the half month of training that was prepaid, though, depending on how the contract was written. (I would expect a reputable trainer to have refunded that money without being asked, even if the contract said it was non-refundable considering the outcome, but that's not really relevant in court...)