I am unable to get a straight answer from UAL, US customs or Canada Customs regarding the passport requirement. I know that you do need a passport to re-enter the US.

My question is can a Canadian Citizen buy a one-way ticket to Canada from Chicago and just show his driver's license and birth certificate. Passport Canada said they can get back into Canada with just the DL and birth certificate. However, will the airline allow them to board in Chicago without a passport?