After not getting OSS when using the new connections facility at YYZ T3 on a WestJet flight from the US, I sent Pearson's customer service a message asking if they had plans to implement it in the future, and got this in response:
You are correct that Toronto Pearson is a One-Stop Security (OSS) authorized airport. This year, we enhanced our OSS program to align with new regulations. We are working with our airline partners to adapt to the new program requirements, and hope to have many more air carriers, such as WestJet, participating in the coming months.