I had a new code on my boarding pass for today's YYZ-YOW flight, which was a connection after flying CDG-YYZ with AC. The new AC code was OSS.
It appeared on the paper boarding card just before the Zone. i.e. it was printed as "OSS - ZONE 1."
On my mobile boarding card, it had "OSS" just below my name, to the side of the QR code.
When I asked in Paris, they weren't sure about it, so I Googled it and found that the EU and Canada have agreed to recognize each other's security procedures.
New airport security option made available to speed up connections for air travellersFebruary 29, 2016 – Ottawa, Ontario – Transport Canada
The Government of Canada is pleased to announce the implementation of a new One Stop Security (OSS) arrangement for flights from Europe and the U.S. connecting through some Canadian airports.
Under this OSS arrangement, passengers and their belongings that have been screened at their point of departure may not have to go through additional screening at participating Canadian airports where they have connecting flights. Making airport connections simpler and faster allows travellers to reach their family and friends more quickly and allows business travellers to get their business done more swiftly. It also helps the Canadian aviation industry attract more flights to or through Canada.
The OSS initiative is made possible when two or more countries agree that their aviation security standards are equivalent.
Existing high security standards found in Canadian airports will not be impacted as a result of OSS.
Unfortunately, it has not been implemented yet in Toronto. When I asked several AC employees (gate agent, lounge staff) none knew when it would come into effect.
[apologies if this has been covered elsewhere on this forum - I searched and couldn't find it]