MS Sasuke wins high difficulty.
Here is the situation, Gaara's sand lack destructive power/penetrating capabilities/piercing capabilities and would fail to destroy any form of susanoo that Sasuke decides to use. On the other hand, Sasuke's susanoo attacks do have some penetrating and destructive power and may be able to break through Gaara's lower level defences which he will start with at the beginning of the fight.
Progressively as the fight goes on, Sasuke will start to feel the strain of the MS while Gaara too will use up quite a bit of chakra but his reserves are greater and his defence and offence capabilities will continue increasing whereas Sasuke's will be reduced. All in all, the longer the fight drags on, the higher Gaara's chances at attaining victory.
Now I believe Sasuke can pull this off with high difficulty. First off, Sasuke doesn't have to spam susanoo from the very beginning of the fight since Gaara won't have much sand to work with and Sasuke's speed is fast enough to contend with relatively low levels of sand via foot speed alone. This was
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but since both Sasuke's speed and the speed of Gaara's sand as well as Gaara's reactions have improved, it is debatable if my statement holds true in part two as well. I say it does since Gaara had
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the 2nd Mizukage's clone. Yes the 2nd Mizukage's clone is
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but Sasuke has also shown many great speed feats which include
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, who should be faster and have better reactions than the no named fodders that got blitzed by the 2nd Mizukage's clone. Not to mention that even Yamato, who is faster than Gaara and the others supporting Gaara commented on Sasuke's speed. Secondly, even Deidara had trouble with Sasuke's speed and
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. That same Deidara early on never mentioned that Gaara's sand is fast which goes to show that Sasuke is still faster than Gaara's sand. Now a lot of people will claim, but Gaara kept up with Madara just fine. However, you should realize that Madara was simply toying with the Gokage and never used his full speed against them. This fact is clearly evident when Madara did not bother dodging Tsunade's punches (
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)(
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) when he is more than capable of doing so. He was merely testing out how powerful the Gokage were.
Even though Madara was fixated on a large number of shinobi, he managed to
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Gaara's sand attacks easily. Sasuke
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with an even faster
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whose slower version without senjutsu managed to
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, a shinobi who is much faster and has better reactions than Gaara.
Alright so the whole point of proving that Sasuke is faster than Gaara's sand was to show that it is possible that early on, Sasuke can slip past Gaara's gourd sand just
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. Replace that kick with a
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which will no doubt slice Gaara and his relatively feat-less sand armour in half.
Now you must be thinking I'm a fan boy for indirectly implying that 3 tomoe Sasuke beats Gaara but I don't think it will be that simple. Most likely, Gaara will be smart enough to encase himself with a
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like he already did during the chunin exams. Now Gaara's sand dome is open to getting pierced either by chidori or by a susanoo sword. Since Gaara's sand defence is much stronger than it was in part one, it is quite likely that chidori alone won't work. I do believe that if Sasuke focusses amaterasu on one point on the sand sphere, he'll be able to greatly weaken it and then take Gaara out with a susanoo sword stab or susanoo arrow. If one susanoo arrow doesn't do the trick it will leave a small hole in Gaara's sand so another susanoo arrow should pierce through.
A lot of people think that because Gaara
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from 5 susanoo clones, no susanoo user can ever breach his defence. This isn't true since as I've already explained Madara was toying around with the Gokage and was testing their capabilities. Gaara reached his limits as he was
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. A serious Madara would then finish him off. Anyhow, what Madara did was slash Gaara with a
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susanoo strike. A piercing sword strike will break through the defence since piercing attacks are better at breaking through defences for reasons I'll now explain. First you must know the difference between slicing and piercing sword attacks. A slicing sword attack is when one swings a sword and a piercing sword strike is a stab/lunge. Piercing attacks are focussed at one point whereas slicing attacks are focussed along a line. Naturally, attacks focussed at a point will have a smaller surface area to penetrate thus they will have more force per unit area(pressure) and there will be less sand at that point guarding against the attack. All in all, Gaara won't be able to defend against a susanoo stab if he had trouble against slashes.
The only way for Gaara to safeguard himself from Sasuke now is to take flight but while lifting himself up, he'd be focussed on attaining an airborne state thus his defences will no doubt be weaker than on the ground. Susanoo arrows can do the trick here after enton has weakened Gaara's sand. If all of this fails, that enton will end up heating up the atmosphere allowing Sasuke to use Kirin against an airborne Gaara. Gaara can not block a massive lightning bolt because it is too fast for him to prepare an appropriate defence.
Sasuke's Counter to Sand Tsunamis
Gaara has to actively grind the minerals in the ground to prepare enough sand to launch sand tsunamis. To turn the battlefield into a sandbox, he has to be on the ground and actively transmitting chakra underground, otherwise, he won't be able to transmit his chakra deep underground to prepare enough sand. If he is in the air, he can't launch a sand tsunami unless he already has prepared enough sand. If Gaara stays on the ground, Sasuke can end the fight relatively quickly.
Anyway if Gaara manages to prepare a sand tsunami and is able to launch it, Sasuke can simply fly over it with his hawk summon. I know the hawk summon can be shot down with sand hail afterwards but Gaara can't use sand hail while using sand tsunami. Sasuke can protect himself and his hawk summon from sand hail with a
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.
Countering Sand Arms
All Sasuke has to do in order to counter
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from underground is to use
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to free himself from their grip and nullify them.
Countering Quick Sand
If Sasuke is being pulled into a
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, Sasuke can summon Aoda or a fodder snake summon to escape getting buried alive. Alternatively, he can free himself from Gaara's grip with chidori nagashi and simply fly away on his hawk. I know Gaara is capable of compromising Sasuke's summons but these sacrificial means is going to allow Sasuke to escape the immediate threat.