DarthParametric - As it has been said, Garrus is only a squad member IF he DIDN'T die in ME2. If you don't import a save game, one would assume that he would be alive as canon.
If he is dead, I have no doubt he will be replaced by some cheap ass turian stand in.
As for loyalty, I hope it works different, but I think loyalty is primarily for RACES. Not the actualy squad.
One Thing I don't want: Last battle - *I CHOOSE YOU, RACHNI! NOW I CHOOSE YOU, ASARI* just like in DA:O..