Originally Posted by dread_specter

I'm sorry for your friend. Air Travel is one of those things that always carries a bit of risk and in this case he got unlucky with the weather.

With regards to 2 things you've brought up ; first, google flights is the absolute worse way to look at flight availability. It is cached data of a not-quite-live AC wesbite, which introduces several discrepencies. Even when you book on AC.com, you'll find that sometimes space is no longer available "live" while it showed availability on AC.com. Google flights is a cached version of that, which introduces an even greater chance of discrepancy.
Also, availability for sale doesn't mean availability. Indeed, airlines oversell. When you get reprotected, you have to be put on guarenteed space. So you might be seeing a flight for sale that really ends up getting you an oversold seat, which isn't acceptable for reprotection otherwise. Or it's just no longer available and the system hasn't reflected.
In any event, the busier flights are generally sold out in the case of irrops and until a flight gets added later or upgauged, it is possible that when you call in there isn't space for you to be rebooked next day. It is in fact a very common scenario.

As far as dialling the UK, if your itin doesn't go through there or you PNR wasn't booked through ACUK, they won't be able to assist. The main resevrations line handles worldwide, and if you did call it then they would've assisted. US and CA flights are all handled by the main res line and those agents won't say that they are based in Can and can't help with US or vice versa.

As others have suggested, standing by at the aiport is a possibility and leaving the file as is also is a good possibility. As flight operations reassess the situation, adding a new flight or upgauging another, your friend will likely get auto reprotected by the passenger repro system.

I also want to point out in response to the post above, if you haven't been offloaded from your flight, your coupon is not available. If your coupon is not available, the reservation agents cannot exchange your ticket, as much as they'd like to. Only airport and another department can offload you, but that department isn't open 24h like the general resevrations, and so it is very likely that when you called there simply wasn't anything that could be done for you.
Always ensure you have spoken with an airport agent before leaving to ensure you have been offloaded and your coupon becomes available again. This will save you some headaches.

Best of luck with the rest of his journey.