In YVR, the separate right-hand exit from customs, then corridor to dedicated connecting-to-domestic security screening has been there for some time. (I used it 6 times in the past year, well before OSS came into the picture). It is a mixed blessing; if queues are short it does actually save time and hassle. But, as others have written, there is no Nexus line so if queues are long it can take longer than exiting to arrivals and going to C departures.

I think OSS is an idea which still doesn't seem to have implementation to match in Canada.

@seat13f_ac_crj - I feel your pain, often do that (Intl-YYZ-YOW), my record being 17 mins from exit from Intl flight to presenting myself at the YOW departure gate. I'm not sure the pax in the seat beside me YYZ-YOW appreciated my sweatiness, though.

You may already be aware - but if the lineup at the YYZ connections security is long and you have Nexus, just take escalator up just to the left of the connections security entrance and use your Nexus to clear normal 3rd floor security more quickly. An annoying extra detour, but often does the trick.