Both sides are going to have to stack the under cards so if it does happen (which I doubt) the fans will win. I would do
Showtime
Mayweather vs Garcia in Vegas,
Khan vs Brook as the co feature from Wembly,
or Thurman vs Marquez or Miadana for a vacated WBA (does Floyd really need it?)
or Broner vs Matthysse (if it does not happen this year)
or Rigondeaux vs Santa Cruz
HBO
Cotto vs Canelo
Rios vs Alvarado 3
Crawford vs Garcia
Need help with the HBO co feature. any ideas
I think Showtime has the ability to have the best overall card (don't see any Haymon fighters going to HBO for a fight on that date).
obviously these are dream matches
HBO
ME: Canelo vs Cotto
UC: GGG vs Chavez Jr
UC: Provodnikov vs Vargas
Honorable Mention/Credit to OP: Crawford vs Garcia
Showtime:
ME: Mayweather vs Khan
UC: Garcia vs Thurman (147)
UC: Broner vs Matthysse
Floyd vs Garcia would get blown away by cotto canelo. Showtime literally can not afford to go against a card that could potentially take away 500k viewers.