I'd say Gaara wins if it wasn't for Gamabunta. Minato would summon it and have it use Toad Oil Bullet, weakening Gaara's sand. Minato could kill himself with Shiki Fujin, and since Itachi would be alive that would mean their team wins. Itachi's finger genjutsu could trap Gaara as well. Those are the only three things the have on Gaara though.
Outside of that, Gaara wins. Gaara's chakra infused sand is fast enough to block Minato's shunshin blitz since it was fast enough to stop Ay, who has a superior shunshin. Gaara is the perfect counter to Minato's Hiraishin, as his ability to alter the terrain will disrupt the placement of Minato's FTG kunai, meaning Minato can never warp where he wants to. Minato can only warp what he or his chakra touches, and I don't see how he's going to touch an entire desert or connect his chakra to it without some medium. Minato also lacks the power outside of Gamabunta to even touch Gaara.
Gaara's sand can block line of sight with Itachi, which would prevent Amaterasu from tagging him and stop him from falling to Tsukuyomi. Sand sensing also means he doesn't even need to look in Itachi's direction. Flying on his chakra infused sand, which is incredibly fast, would allow him to evade Totsuka and Yasaka Magatama. Gaara could easily sink him beneath the desert. The only thing Itachi would have going for him is his finger genjutsu that Gaara cannot stop and has no feats of breaking a genjutsu of that level.