I have shot my entire project with the HVX200 ( squeeze ) ( dv ) but need to shoot with two cameras soon. The second camera will be an old Dvx100 ( no squeeze option )

I assume i'll need to make some fixes in post but what should I shoot the dvx100 at in order to match the hvx200 squeeze footage? 4:3 or letterbox?

Both cameras will be shooting 24pa

As far as I know, the anamorphic option on the DVX is simply cropping and stretching vertically. Might as well just shoot 4:3 and crop later, since you wouldn't lose rez and you could reframe if needed.
Put some black electrical tape on the LCD and you've got the framing set.

Letterboxing would work the same way, but that would gain nothing, and lose the option to slide vertically later.