The CGDGCD tuning is also known as Csus2 tuning (a Csus2 chord is what you get if you play all strings open).
This tuning is primarily recommended to try on an acoustic steel string guitar. This is one of the many open tunings that are suitable for songwriters and by utilize many open strings, original and beautiful sounds can be found.
The name of the tuning tells how you should tune your guitar, in other words C G D G C D. The 6th, 5th and 1st strings should be tuned down and the 2nd string should be tuned up. There are risks involved of breaking strings when a string is tuned up from the standard, but since this is only a half step, a healthy string should manage the extra tension.
Including an octave perspective, the tuning is written C2-G2-D3-G3-C4-D4, meaning that the lowest string is a C note on the second octave, the second lowest string is a G note on the second octave and so on. Standard tuning reference: E2-A2-D3-G3-B3-E4. Open C tuning reference: C2-G2-C3-G3-C4-E4.
The xx7000 version of Am11 is without the fifth. Instead of Cmaj9/E, Cmaj9 can also be played as 042000, but in many cases it will not sound very well with the low open C string included.
Other sus chords in CGDGCD tuning
There are lots of possibilities for playing sus chords in this tuning. Some additional options are:
More chords in CGDGCD tuning
Assorted chords in this tuning:
Chord progressions with CGDGCD tuning
Some examples of progressions using this alternate tuning:
Cadd2 - Dm11 - Cmaj9/E - F6/9 - Gadd4 -
Cadd2/4 - F6sus2 - Gsus4
Csus2 - Bm#5 add(m2) - Am11