Saca's candidacy will make the 2014 a real three way race among Saca and Salvador Sanchez Ceren, the current vice president from the FMLN and Norman Quijano the ARENA mayor of San Salvador. I think in a two way race, Quijano would have easily beaten Sanchez Ceren. The question is whether a Saca candidacy will split the right wing vote. In that case, the most likely outcome would be the requirement of a second round election between Quijano or Saca and Sanchez Ceren. In that second round, my early guess is that we will still see one of the right wing candidates win. Quijano is very popular, and Saca had relatively high popularity ratings throughout his presidency. Sanchez Ceren just does not have the personal appeal of the other two, and his origins in the hard left of the FMLN make him unattractive to moderate Salvadoran voters.
But we have 15 months of election campaigning before we know the real answer.