In past when I've looked at travel to Europe from here, there's always been a significant premium (a) for travel from Charlottetown (over Halifax) and (b) for travel to anywhere other than London Heathrow.

Much to my surprise, it looks like the usual Charlottetown premium is much less during the current Air Canada seat sale than usual. For example, the best fare on the Air Canada website for Halifax to London is currently $448, while the best Charlottetown to London fare is $600; usually the difference is three or four hundred dollars, enough to make the drive to Halifax worth it.
Similarly, it looks like travel to places in Europe other than London doesn't demand as much of a premium either; while Charlottetown to London is $600, Charlottetown to Paris is only $718.