I don't think Floyd would still be unbeaten. As good as he is, I can't see him beating prime Tito, Oscar and the Chavez that Pea fought. Vasquez would have been a tough fight too, given the size disparity. McGirt would be interesting but I'd favour Floyd. I think Floyd would beat his other opponents too - Nelson, Haugen, Ramirez etc. Although Oscar at 154 would be tough for Whitaker (since he was never meant to be at junior-middle) given how close he took a prime Oscar at 147, I'd have to favour Pea to take this one. I'd heavily favour Whitaker over Floyds other opponents.
Much like Whitaker, I don't see Mayweather losing any fights (legitimately) until the mid or late 90s. I can see Chavez beating Floyd at lower weight classes, but at 145? Floyd's style is more suited to be successful at higher weights like welter than Chavez's style. I'd confidently pick Floyd to beat the 1993 version of Chavez at 145. Mayweather-McGirt would be a good match of fine technicians, but I think Floyd wins that. Floyd at 147 against prime versions of De La Hoya and Trinidad, especially after having fought professionally for 13-15 years like Whitaker did, now those are very tall orders for PBF. We'll leave out the fight with uncle Roger.