I am in the USA, so I am not really familiar with how Canada's system for providing services for students with special needs works, so what I am going to say may not apply at all to your situation in Canada. My apologies for that in advance.
I am a teacher (I promise we are not all horrible people

). The school district asked to do special education testing on my middle son at the end of his kindergarten year. I was not at all surprised by the request as he had significant language delays and severe fine motor deficits. In the course of testing, the psychologist noted definite ADHD tendencies in addition to the other issues, and as a student with ADHD he has been served through special education ever since. In the United States, what that means is that specific goals and accommodations are put in place in order to assure that he is worked with and provided for in a manner that gives him the best opportunity to have success in school. These accommodations are legal mandates, which means his teachers MUST make these accommodations according to law. Does Canada have a similar legal guarantee in place? It amazes me that you were going to have to pay for his testing.
The schools have done a wonderful job of suggesting ways to help him succeed in school. The teachers, up until this year (he's in 10th grade now), have always followed is accommodations. His pediatrician at one point wrote a letter making suggestions for accommodations that could be helpful. When I forwarded it to the school, a meeting to review his accommodations was immediately scheduled to review his current plan and to be sure that the doctor's suggestions were put in place.
This year, unfortunately, he has run into a couple of teachers who for some unknown reason believed that they had better ideas than what his legal accommodations stated. Boggled my mind because I work in this district and not following those mandates is a HUGE no-no. I hated to do it, but I called them on it. The school diagnostician immediately ordered a meeting, knowing they were out of compliance, and his accommadations were reviewed, updated, and strongly enforced (to avoid a lawsuit even though I doubt that I would sue my employer). I guess I'm telling you this long story because I'm not understanding how your son's educational needs are not being legally enforced in Canada.
My son is not a gifted/talented student, but your son sounds like he might could be. In the USA, every district must have a program in place for assessing and serving gifted/talented students. You need to see what is offered in Canada and insist that he be evaluated. Gifted students think differently, work differently, and even feel differently. His behaviors in school could be characteristic of those traits. In our district, testing is done only a few times a year, so you might have a wait before it is done, and he might not qualify (the criteria are rather complicated), but it would be a shame if these issues are due to not being served in the right educational setting.
We did choose to start our son on medication at around age 7. It has helped him immensely over the years. He initially was inattentive type. What we saw in elementary school was intense distractability. If the landscapers were outside mowing the grass, the noise alone would pull his attention away from everything going on in the classroom, for instance. As he got older, we did start seeing more hyperactivity traits: pacing particularly. Never defiant or misbehavior though. He has horrible organizational skills which has been his greatest problem as he has gotten older and has had to juggle several teachers. He has always found that the medication lessens the intensity of his symptoms and he is the one who lets me know when his prescription is about to run out because he realizes how much more difficult things are for him without it.
If Canada doesn't have a system like I've described, sit down and write out what specific, workable accommodations that seem to be helpful to your son. Better yet, if he has a pediatrician or therapist who can write a more official letter, it would carry that much more weight. As much as you are frustrated with the teachers, you have to find a way to make them your allies. Hear their input. What we see happening in the classroom is often remarkably different from what parents see at home. That is not an indicator of failure on anyone's part necessarily. Some kids really do a kind of Dr. Jekyll/Mr. Hyde thing on us. It's always hard to understand why that is, but it is a very common phenomenon.
Well, this has gotten really long. My apologies for that. I hope you and the teachers are able to work together for your son's best interests.