Just flew SJC-YVR-YYC yesterday and can confirm that OSS on my boarding pass made absolutely no difference at all to security screening. I still exited the transborder area and had to go through the main YVR security screening process. I had Nexus, so that sped it up. I actually did not know what OSS meant until I came to Flyertalk later, but no Air Canada agent seemed to know what it meant either.