The carriers at YYZ (with the exception of AZ) are pretty much segregated by alliance. If you
are arriving on a *A flight (T1) and travelling onwards on OW, Skyteam or WS (T3), it's unlikely to be on a single ticket - in which case you probably will have to collect baggage &c anyway, so an airside transfer wouldn't really be an option.
And I'd hardly characterize myself as AC-centric ; EC-centric perhaps...