I actually have several birth certificates. One from the province on NFLD Canada, one form the Basilica of St John the Baptist and one from the actual US AFB hospital.
Anyhow this was in 1958.
As far as my son joining the NC national guard and them wanting my proof of citizenship, I guess they just do extensive background checks now on recruits. Not sure if it would have mattered, but they did.
But I will get out my naturalization form and see exactly what it is and follow up.
Only one of them will be a vital record kept by a legally-recognized entity. Probably the provincial government, which is the entity that can issue a "certified copy."
Did your mother get her citizenship when you were five or six? You may have been at her ceremony and the officials were just being nice to a restless little boy by letting you say the Pledge too.