Itachi takes this mid-high diff.
-Crow clones can be an effective counter to Gaara's distance, and he has no knowledge of them. They can scatter and reform near Gaara, and potentially use genjutsu on the astonished Gaara.
-Amateratsu isn't being stopped by Gaara's sand. His sand armor is his best bet, and even then, the black flames being on his sand armor could leave him vulnerable to crows reforming from behind.
-Third eye is linked to the optical nerve. If anything, it makes the genjutsu threat greater. A tsukiyomi would end this match with ease.
-Gaara's sand isn't quick enough to catch Itachi. Mu was capable of evading it with his sensory and decent speed. Deidara was able to outspeed it with his C1 Bird, which was depicted to be slower than Hebi Sasuke, who was slower than Itachi. Bee was being recurrently inferior to Itachi in terms of speed. Itachi should have no problem getting away from any sand threat, or in the case of a sand tsunami, use his Susano and its constituent Yata mirror.
-A Fireball Jutsu infused with Enton flames, like the one used against Sasuke, could also end the fight. The manga portrayed any Sand in contact with Enton to eventually fall onto the ground, likely because the Enton's flames would've eaten through the chakra holding them up. A continuos attack like that would mean any sand would drop to the ground after attempting to defend Gaara, while any sand armor in contact with Gaara to also end up on the floor, only to leave Gaara grilled.
-Itachi could choose to use his amateratsu, bunshin feints and himself as a strategy to land a genjutsu. Amateratsu is fired at Gaara's face and isn't reacted to. Gaara temporarily has no vision while the black flames are right in front of his face. Crows begin to reform behind Gaara, unnoticed, as the sand armor is being dropped to the ground. Once reformed, Gaara will either be taken by surprise, or will notice it at the last second, and look at the clone's eyes (or hand) to end up suffering a redeeming genjutsu defeat by the one and only, Solo king.