I have been on this flight (AC 860) several times and each time the LHR-bound passengers have not been allowed to disembark. There is only a ~1 hour groundstop in YYT and it would be very tough to unload and reload a full 767 with the space and manpower YYT has. Additionally, I don't think there is a sterile area in YYT's terminal...

The last time I was passing thru YYT from LHR to YHZ on AC 861, I was asked to show my boarding pass in YYT to flight attendant to confirm I was indeed a thru pax.

When I first started working at AC in YHZ, the domestic leg of 860 was impossible to ticket independent of the int'l leg... there was a narrowbody flight (usually DC-9 or A320) that departed for YYT almost at the same time that carried the domestic traffic; I think the flight number was 620-something.

Only during bad-weather IROPS when we had a nasty backlog of YYT-bound pax would the managers let the YHZ-YYT leg go non-sterile to get those folks home. In these instances, the duty free goods the LHR-bound pax had purchased would be stowed in the bulk hold until they got to YYT and the domestic pax offloaded. Now I hear that practice is the norm and the domestic leg of 860 is open for general sale.

Sometimes it's all for naught anyway as this flight overshoots YYT altogether in the winter due to weather I'd say a minimum of 6 times a season.