It's a question best answered by whoever will convert the video to film for you. Your best bet may be to hire an Anamorphic Lens (try century optics), or shoot with some kind of guide to where the cinema framing will sit within the 4:3 frame.
Cinema release is a very big deal though, so I guess you must be very new to this. You need to find out the available ratios in the cinemas that you will be showing at (there are a lot of film ratios)
Try shooting in 16:9 so at least you will be compatible with digital TV, and it will provide a good widescreen format starting point, to convert to a cinema format.