The Guard schticks do a very good job of representing the different forms from a gameplay perspective, I think. My interpretations of each guard with combat forms is as follows:
Balanced Guard
A mobile posture using speed, agility and a good sense of balance to keep out of harm’s away as you deal with your foes.
From the description, it sounds like a good choice for Soresu/Ataru.
Focussed Guard
A defensive posture, particularly effective against one target you have picked out as dangerous.
This one definitely strikes me as representing Makashi, with the focus on one target, but the overall defensive nature can also be indicative of Soresu.
Forward Guard
An aggressive posture, seeking to advance against your enemies and destroy them quickly.
Just about any of the offensive forms fits this Guard, and it's tap strikes me as significantly Vaapad in nature.
Orthodox Guard
The standard sabre Guard as taught at the Temple, defensive but looking for opportunity to make a deadly strike.
It's the descriptor of it being the standard that makes me see this Guard as primarily Shii-Cho, though being the foundation, it can certainly represent the blended forms easily enough, I think.