Canon EOS 5D MK III "live view"

There's a third party firmware upgrade for the Canon 5D Mk III that gives focus peaking, which might be useful to you.

http://www.magiclantern.fm/whats-new/104-releases/143-second-alpha-for-5d-mark-iii

It's only an alpha version ( still under revision prior to release ).

I can't comment on how well it works or not, but the Canon 5D forum may be better placed to help you.

If this is important to you then you might also consider getting a camera system that supports focus peaking.  The Sony NEX models and some higher end A-models support focus peaking and their is a metabones adapter allowing AF for Canon lenses on NEX models.

Also if critical focus for macro is important a good old fashioned focus rail may be very important.

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StephenG