Can a Canadian citizen submit their Hungarian Passport application in the USA, at one of the Hungarian Diplomatic Missions?

Yes, all Hungarian Diplomatic Missions world-wide (Hungarian Embassies and Hungarian Consulates) are authorized to handle the passport applications.

Please note, the passport application can be submitted only in person; the Hungarian Missions take passport applications by appointment only; if you are setting up an appointment in a third country (e.g. if you are Canadian and you plan to submit your application in the US) you may have a longer wait time for the appointment than in your home county.