Originally Posted by
Garbageman
A family member with no status flying this year in a similar situation (arriving on international J, connecting to a domestic flight that was Y-only) was allowed access to the lounge at a different Canadian airport.
Was that at the final arrival airport, or at the connection point? There's a big difference. A J ticket (I believe it's the ticket, and not the "boarding pass", that gets you lounge access?) entitles to you departure lounge access.
Connecting in YVR on YYZ-YVR-YYJ gets you lounge access, even though YVR-YYJ is in Y, because you're on a J ticket.
Connecting in YOW LHR-YOW-DCA does not, because the domestic lounge would be an arrivals lounge, and there is no transborder lounge.
However, as has been mentioned above, you can always just try. The worst they can say is no.