It would be silly to try and compare the miss deeds of Cantona and Barton, while both obviously has a dark side, while I was never a fan of Cantona he never rose to the level of criminal activity Barton has (mind if the kicking of fans happened outside of OT, maybe he would have done some time).
Also, I don't think you can compare them on talent. As already said, I'm no fan of your former Gallic talisman, but there is no doubting his talent which is on a far higher level that Barton's best day.
But have to ask the question, at what point do you forgive and give a player a second time. For superstars that level seems to be lower, but while in no way trying to cover up the despicable things Barton has done, has he become a convenient punching bag? Fact is he's been out of trouble for a while, from what I understand stopped drinking completely, and there is no denying he was a central figure in bringing Newcastle back from the Championship and helping them get to mid table last season. At what point after someone has done their time are they actually given another chance?
But end of the day I actually hope you don't take him. He's not going to solve your midfield situation, and while Sniejder is a risk being unproven in the prem, he's a step above Barton in terms of quality, but Barton is better imo that what you've got. Yes he has risks, but I think those days are behind him, and I doubt a seasoned manager like SAF would put up with it if it did surface again. Actually the biggest risk is not what he might do down the high street after hours, but whether he unsettles the dressing room, which is maybe why Newcastle are giving him the boot, but actually I think its because he's hit a nerve with his Twitter account and its the Toon Board room he's actually embarrassed. So actually maybe a good fit with you lot as your board I don't think can be embarrassed, or at least has proven they don't care to listen what is said about them from fans, so a loud mouth player I doubt would bother them.