Gaaa^San
Back before the time skip I'd still agree Gaara could beat Sasuke, basically because Sasuke's sharingan had not advance a whole lot, and his only attaack that could penetrate Gaara's sand was the Chidori but seeing as he has no Bijuu (or however it's spelled) he had no massive enrgy reserve and could only perform it to a limited extent... We all did see him get beat down already following the Exams but if you skip ahead to the times now, it's a whole 'nother story....
Here, yes Gaara has advanced to the level of Kazekage but regardless here we have Sasuke with the most advanced form of the Sharingan bloodline..Mangekyu (Or however it's spelled :S) Anyways, we all can see this is incredible just because of Itachi.. Sasuke has now a variety of abilities at his disposal (assuming he's actually done a lot with those three years) to pick away at Gaara's fragile mind, and still his physical ability could be even stronger seeing as we havn't seen much of him yet... WHY DOES EVERYONE THINK THAT SASUKE HAS THE DAMN MANGE SHARIGANS!?!?!?!?!
He does not, he only has level three.
Plus, he could only use his abilities close up, Gaara could just dump a section of desert on him at this point and be done with it.