The US requires precisely the same documentation for entry into the US as was needed for entry into Canada. There was a proposal to require passports from US citizens but that change has not gone into effect (yet) and judging by the reaction may not go into effect for a long time. So there was no need to obtain an expedited passport for the trip to Canada; but now that the birth certificate is "gone", he cannot leave the US. Rather ironic that applying for a passport has resulted in a "more restricted" status than before the application.