If Pacquaio has real intentions of fighting and having a chance against Mayweather than Cotto is not a good choice of opponent whilst Floyd serves time.
In fact why are other opponents being discussed in the first place. Didn't Arum say Pac's eye needs to heal, and that June/July was when we were likely to next see Pac in the ring again. That's plenty of room to promote a fight with Mayweather. That's of course if Arum was telling the truth.