It just wouldn't make financial sense to have all 3 fighters on the same card. But to answer your question, the main event would undoubtedly be Mike Tyson.
If you look at the history of the ppv records https://en.wikipedia.org/wiki/Pay-per-view#Boxing Tyson fights were all generating the same revenue as mega fights or breaking ppv records. Stands to reason that with the same Hype he had back then now he could do Mayweather / pac, Mayweather / mcgregor numbers regularly and even more.
