Thanks for the interesting insights and information. The cancellation of the direct flight from London makes sense of the 787-9 for getting people to YOW. (thanks for the correction on the correct way to address the aircraft) if they could ship affected people from London to Toronto - I know the 0900 departure from london would manage this connection Not sure what the usual loads are from LHR to YOW but it was midweek.
I am used to running subway systems and they don't have loads of trains sitting about either. But any mover of people - coaches, bus, trains, airlines, ferries rarely operate without spare vehicles. With subway vehicles, a 10% float of vehicles is needed for steady state maintenance on a mature fleet with a spare or two for casualties.
The fact that AC is receiving the max but not retiring the equivalents show they're either increasing service or struggling with aircraft availability. BA who now have 5 x A320Ns are yet to retire any aircraft on a like for like basis, to allow for route expansion with the demise of Monarch Airlines (a UK LCC) and a rehab / densification programme of the existing fleets