i would like to understand how to improvise over a Modal Sus chord progression.

As an example you can look at the video down here at 3"00. There Begins a Improvisation by a Keyboarder and later a guitarist over a chord change with Sus or slash chords.

I think the Progression is Gmaj/A , Ebmaj/F , Cmaj/D , Cmaj/D
What would be the right way of thinking about this Progression?
What scales or Arpeggios should be used for Improvisation?

http://youtu.be/avibOW6YTI0