It is unclear to me who "they who purchased the tickets are. My own thoughts are that I would be asking them why the OP was booked on a Low Cost carrier when there are flights by Air Canada between the same points. It may well be that AC would have had policies in place that would have alleviated the OP's inconvenience. Why did "they" book the OP with BA in the first place when they could have flown AC all the way from LHR? I can only imagine that it was dearer as it does not make sense to me.

I think, like the others, that this is an insurance issue. Shame.