Upgrade or Transition? I assume you mean Transition (from the right seat of the ERJ to the right seat of the A320)? I am not certain and things are subject to change, however, as best as I understand it and seeing as they are bringing in very qualified guys (and gals) to staff the Embraer, expect two years of commitment on that type.
Makes no sense for a company to search all over for experienced and type-rated Embraer guys then transition them to another type a few months later. What they have made clear is that these pilots will have a future at Gulf Air after the Embraer goes (we are getting no more and decided to order C-Series instead).