Registered Psychotherapists in Ontario do not formally diagnose ADHD. That is the role of a physician, psychiatrist, or psychologist with the relevant training. What we can do is sit with you in the question of whether assessment is worth pursuing for your situation, and refer to assessing clinicians when it is.
We work with self-identified neurodivergent clients. You do not need a piece of paper to be taken seriously here. If your experience tells you your brain works differently, that is enough to begin the work. For some clients, formal diagnosis later becomes useful, whether for medication access, workplace accommodations, or simply for their own clarity. For others, it never becomes necessary. Both paths are valid, and we can support either one.