Asking on behalf of family member. They are a US-British dual citizen. The US passport was sent for renewal and processing has been very slow so they have no passport now except the British one. They also have a valid US passport card in hand. There is upcoming travel to Canada. Could they use British passport to enter Canada by air? Seems they would need a ETA from Canada for the British passport? Would they be able to reenter the US by air without problems? They are considering flying into Buffalo and driving over the border with the passport card to avoid problems but this would be very inconvenient. Would appreciate any advice.