Originally Posted by
aerobod
YYJ-YYC-YHZ-GLA is only an hour slower than the quickest route which is YYJ-SEA-KEF-GLA, but crossing two additional borders and having to arrive earlier for US pre-clearance will eat up much of the time saving and add risk to missed connections, especially as WestJet and Air Canada are the only airlines that can provide an end-to-end journey on their own metal both taking about 15.5 hrs, all others require codeshare.
There's no preclearance in YYJ
Even sticking with WS partners, DL/KL via SEA/AMS would be much better as you have a 10 hour flight to get a proper sleep on.
Next best option within the WestJet partner environment would be YYJ-YVR-AMS-GLA on WS/KL. Longer layovers but again a proper 9h30m flight to get some rest on.
The WestJet option is a 1.5 hour flight, 2h49m hour layover, 4h46m flight, 1h34m layover, 5h24m flight. That's what I meant by painful. No way someone can fly that itinerary and be able to feel rested upon arrival.