It's going to depend entirely on your doctor, really. My doctor required that I have a letter from a mental health professional, but I was able to find a sympathetic counselor, and since I'd already been living full time as male for over two years at that point and didn't really have any issues I needed to work out, I only had to see her once or twice before she wrote the letter, and my doctor was okay with that. It was more of a formality than anything. Some doctors will prescribe T based on informed consent, without a letter, and some won't; likewise, some therapists will be flexible and not put you through a required number of sessions, and some are going to be really strict about seeing you for a certain amount of time.
Also, there are a few surgeons out there who don't require a letter. I believe Brownstein is one of them, but I might be wrong about that.
EDIT: I just read that you live in Canada. What I said is true for the US; I have no idea how things work in Canada. Sorry.