Honestly, what I've seen and heard of FFXII has pretty much detered me from playing it anytime soon. The battle system looks weird and neither the characters or story look very interesting. I enjoyed 10 somewhat, but I prefered both 7 and 9 to it out of the ps games.
Unfortunately for Cloud, he's a victim of his own popularity. He was such a great character in FF7, but while I like his new look and has an awesome fighting style in AC, they really have butchered his character. They seem to have decided to cater him more to the masses by giving far more angst than he previously had (emo characters generally seem to a big hit in Japan from what I can tell), and is just thrown into our faces so much now even I get sick of him, and I am (and probably always will be) a fan of his. It's really because of this that, while I like him and admit would try and main him if he was in, he really shouldn't be in Brawl.
The only problem is that he is pretty much the biggest FF character they is, and SE knows this. Part of me feels that they may try to push Sakurai into including him, especially if they realise he is technically eligible (in a very minor cameo role in what isn't even a FF game). Fortunately, it seems like Sakurai is more interested in Geno, so I guess it really depends on who presses harder (and I'm pretty sure Sakurai would be the one who get's his own way). Also, it's possible they may overlook (or not notice, it is a pretty forgetable role) Cloud's appearance and opt for one of the earlier FF characters. FF6 seems the most likely, seeing as it's one of the more popular games, and was the last FF game on Nintendo before they moved to Sony. However, FF4 is getting a DS remake, so who knows (though, personally I've never had much love for FF4).