The fact is there is no availability ex YYC/YVR or YYZ today due to the high volume of ex Zoom pax requiring flights across to the Uk and Europe also the flights are busy as many schools start back on Monday. There are quite a few flights tonight that have fare paying pax on standby .
As someone has said BA is not a charity and would only give away seats to Zoom's crew if there was seats available. Sadly theres not.
If they can't get on BA flights due them being commercially full why don't they try another airline. BA isn't the only airline to fly to the UK from Canada and USA.
Infact Air Canada has flights today from YYZ/YYC and YVR
Flyglobesoan has a flight with seats ex YVR to LGW.
From JFK VS/AA/DL/AI and KU all have flight to LHR today