Maynard is the clear favourite, but you never know in MMA.
I can't see what Guida would really do to him though. Guida has exellent grappling but Maynard is still the better wrestler and Guida won't be able to push him around or lay on him.
Guida doesn't really have much technical striking but he makes up for it with chin, cardio and movement. I think Guida frustrates Maynard a bit and will make it a hard fight like he always does, but will eventually lose either a TKO or decision. I have a feeling Guida will bounce around trying to avoid big hits but will eventually get caught and hurt.