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A chord is described as 'sus' or 'suspended' when it has a 2 or 4 instead of the usual 3. So the most simple sus chords (the ones guitarists play) are: 1-2-5 and 1-4-5
Jazz heads have take things a bit further. Usually a 'sus7' chord will be read as meaning "play root (and fifth) plus the major (or major 7) chord built on the b7th", so the sus7 chord will be: 1-(5)-b7-9-11(-13)
Standard scale choice
To get the suspended feeling across, use the major pentatonic built on the b7 of the chord.
Alternatively, you could 'decide' whether you want to imply major or minor tonality, and treat the sus7 chord as a dominant 7 (mixolydian mode) or minor 7 (dorian mode) instead. I tend to think that it sounds better treating it as a minor 7 in rock contexts, and as a dominant 7 in jazz, so maybe you should try both. Some modern players will even include the major 3rd in the chord voicing (e.g. at the start of Miles Davis' version of Someday my Prince will Come), so it's best to listen out for the rhythm section here.