...have new units for each race available at multiplayer ? I found somewhere this link that says so but i am not sure : http://www.teamliquid.net/forum/viewmessage.php?topic_id=118037
Seeing as you took that link seriously, I doubt you ever played starcraft Brood War? They'll add more multiplayer units. Probably a lot more campaign units as well.
I think it will be very similar to the terran campaign, some will be added, most will not. I hope the expansion isn't $60, but that may be too much to hope for.