4 years ago i overstayed a visa waiver, i now travel to Canada on a regular basis with no problems, but now a cheaper flight is wanting me to go through IAD airport which means touching USA soil, my question is, will i have to go through border control or just stay in the airport and not go thorugh a visa situation. Ill be going from Heathrow one stop dulles and on to Halifax , NS.

Very few US airports have a separate international area where you can transfer to another international flight without going through US immigration. Dulles does, as I remember, but I don't think there is any guarantee your flight will go there. If you arrive at a gate that is not part of the restricted area, you could pretty much go anywhere, so you must go through customs.

You could check with the airline to see whether you will have to go through immigration. However, you always run a risk of the second flight being canceled and being stuck in the US overnight or something.

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