I live in Seattle for the last 5 years. For some reason, it is much much harder to google content in Canada. It always come back with a USA story somewhere.
I have link another forum of Canadian PRO. They said that the Ontario building code permit UC1 and UC2 treated wood. But if you read all theses PRO, many will tell you that you should only use it for the base plate or not at all.
I have found a similar one in Québec French... They don't want much treated wood at all. However, these text do not "Google translate well" at all. Suffice to said that "Préservative" get translated by "Condom" and the house have ED problems somewhere.
The origin of the crisis in Québec (Around 1998):
I know their was an accident in a camping ground in Québec. Somebody (a tourist) was burning some CCA treated wood -- and a child playing 100 feet away or so needed to be rush to the hospital. I don't even know why: Was it some allergy -- was it poisoning? I don't know,
Then, a few week later, a fire started in a very large out building of Québec Sépaq (National park). The firefighters rushed to the blaze and later, we learned that 2 of them were treated for mild poisoning.
This started a very big talk in the French population. A lot of pressure has been put on Rona (similar to HomeDepot -- Now own by US Lowes) to find alternative and remove CCA treated wood from the shelf -- and they come back with Plastic Deck and others stuff -- but CCA wood remain on the shelf for a few more years.
By itself, the Canadian (and Québec) Government was somewhat slow to react -- mostly refusing to recommend any treated wood alternative has safe. They emit a statement, something to the effect it is safe when use outside and don't let your toddler crawl on it.
Finally, especially in Québec, Many believe the US EPA when it said a product is dangerous... but they have no confidence in the EPA when it say something is safe. Go figure.
Anyway, this become a very big stuff including "Water Pollution", risks for fireman, Risk for Wood Worker, Risk for mills worker, etc... Many university researcher have talk a lot on TV. A lot of law/code have been changed.
Some locality in Québec might have gone overboard. (Or they imitated a New-York emergency because of asbestos -- who knows)
Here another person that seem not to use Treated Lumber systematically:
We can use any of that and we never use treated lumber.