Does the Air Canada flight from Ottawa, Ontario to London, England fly over the United States of America?
Is there any City in Europe that Air Canada flies to from Ottawa without flying over the United States?
Ottawa-London: Probably enough for passenger overflight rules to be an issue. If you check AC888, it regularly overflies Maine. Also, it's not only overflight, but nearest suitable airport is also a concern.
WestJet flies from Halifax to London Gatwick. This is quite well east of the United States, but you'd have to confirm with WestJet if they will allow bookings by persons on a US no-fly list.
You'd also have to get to Halifax without overflying the US.