Csus2 to Em

The Csus2 → Em transition is the same IVsus2 → vi move in the key of G or any key where you're playing G shapes.

Chord shapes

Play the Csus2 chord in a G shape and transition to Em.

You could keep your third and fourth fingers on the high strings to play an Em7 and maintain the Csus2 sound into the Em7 chord.