H4 for a canadian baby

Hi,
I have been trying to find an answer to my situation, but couldn't find the exact answer.
I am a non-Canadian working in Canada and will move to US with H1B visa. My son is born here and thus a Canadian.
Does he need to apply for the visa interview along with me for his H4 visa
or can he just get H4 status at the border?
If he can get H4 status at the border, how much is the processing fee?
Any information will be greatly appreciated!!

You can do it either way, at the border it will be $6 for the I-94.

Thank you very much for the info.