Question on Application for Proof of Canadian Citizenship

Hello there,

I am new to the forums and in the process of applying for my Proof of Canadian Citizenship (I was born and raised in the US). I've taken the online "test" that indicated I am most likely a Canadian citizen because my father was born there, however I've run into a simple question on the application that has me a bit perplexed.

A little background; My Father was born and raised n CA, left the country when he was around 25, in 1950ish (I don't know the exact date he left CA). He was living in the US when he met and married my mother (born, raised and a lifelong US citizen) in 1956 in the US, and spent the rest of his life living, working, paying taxes, raising a family, business owner, and paid/collected social security, before his death in 2003.

With that background, the question that has me perplexed on the application asks, "Is he, or was he, a citizen of another country?"..and..."If yes, when and how did they become a citizen of that country?.."

I would like to say, yes, my father was a US citizen based on all the information above, BUT, I am not sure. I don't know if he ever got a US passport, or was naturalized a US citizen. Would I be better off just answering "No" to the question since I am not sure?

I just want to be as accurate as possible with the application information, since it's such a long process.

Any advice would be appreciated...