You bring up an interesting point re: domestic cougars. In this case, however, I really do believe that there are wild cougars somewhere in the province of Ontario and that the ones in question aren't ones which have been released by their owners/handlers. Also, with regards to cougar sightings in the Rouge Valley, there are way more than 1-2 over the last 20 years. I don't know the exact numbers, but I know they are greater than that and not all of them correspond to escapes from the zoo, which number I believe 4 during that time period.
With regards to people who mistake another animal for a cougar, I don't know if I agree with that. In my opinion, there really isn't anything out there that could pass for a cougar, apart from maybe a very large golden retriever. With that being said, there are still plenty of differences between the two such as coat length, tail length, and musculature. I'm curious as to what type of animal you believe is being misidentified?
Finally, I do put a lot of faith into what the Ontario Puma Association says for a couple of reasons - they are an organization which is specific to the research of the cat and no other species of animals, and it is clear that they work closely with the MNR to find hopeful evidence of the cougars existence here in Ontario. It is the same feelings that I harbour for the Canadian Peregrine Foundation, of which I am a member.
Cheers, Attila