In piano chords is cadd9 the same as csus2?

No. A Cadd9 is just what it sounds like: a C chord (C-E-G) with a 9 (D) added. Thus, it is C-E-G-D. You will *not* want to play it as C-D-E-G because it will sound like mud. A Csus2 is a *suspended* chord, which means it drops the third. Thus, C-D-G. Suspended chords, by their nature, generally feel unstable and strongly pull you to wanting to "resolve" them back to a "regular" (non-suspended) chord, most usually the major. Suspended fourths are probably more common than suspended seconds (Csus4 would be C-F-G). A Csus4 strongly pulls you to a regular C chord. To complete the discussion, there's also the C9 chord, which illustrates the weakness of normal chord nomenclature. The name C9 *sounds* like it ought to be what Cadd9 actually is. But in fact, a C9 implicitly also has the 7th. So it's a C7 chord, plus the 9: C-E-G-Bb-D. It's a great "bluesy" chord.