Well, personally i think it gona be a quite a intense battle but sasuke has more chance of winning say (55+%) if gaara is not in a desert
This is my analysis:
1. yes gaara can block amaterasu read this:
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even if he cant he can just use replacement jutsu.
2. Gaara's sand shield took nearly five wallop from madara's swords before breaking so its quite strong to stop projectiles.
3. Gaara can pull sasuke away from the ground just like he did madara
4. ems techniques take a lot of chakra, but sand techs are relatively less taxing.
5. gaara can fly now so no chidori.
Conclusion: Its not gona be a easy win, first one to make a mistake will die and sasuke tends to underestimate.