Sasuke should win ultimately his speed was enough to break the sand defense with 2T and with 3T + CM1 + CM2 mastery his speed with quickly overwhelm Gaara and the curse mark also increase his sharingan precognition so he will own him. If Gaara has giant bijuu mode he wins though
Sasuke wins if he can end the fight before Gaara starts transforming into Shukaku. If not it's low med diff for Gaara. Otherwise Absolute defence Base Gaara gets beaten.