I went to my optometrist/optician to pick-up my prescription, with the intent of using it to buy contact lens online.
I was fully prepared to do battle over who owned the prescription, expecting some resistance from them to enabling my shopping around. A little bit of Googling Canadian Privacy Law, a couple of all-nighters writing up my argument, and I was ready.
In the end however, clearly sensing my determination and preparedness, they caved immediately - handing it over without even a token protest.
I don't envy somebody else in that situation lacking my grasp of the legal & identity issues.