I think that Naruto and Gaara would hold up very well agains Itachi's technique. I think that their demons would protect them. If Itachi tried to hypnotize them and enter their mind so to speak, he would have to deal with the Kyuubi or the Shukaku. Even Itachi could not handle the power that those two have.

I think it would be something like Inner Sakura beating Ino's mind transfer technique. Obviously at a much higher level, but still simmilar.

I am not saying that Itachi cold not beat these two, but I do think that he would have to do it some other way.