I can't remotely see this happening. That simply is not the way politics works. You would have 2 Hispanic American sons of Cuban immigrants.
It would be like Hillary choosing another old white female to run along side of her.
I am not knocking the choices, just can't see it happening.
If it's Rubio (which I think is most likely and who I'll personally be voting for next month barring disaster), you can just about bet the house Kasich will be the VP selection. There's a possibility Nikki Haley or Suzanna Martinez might get it, but I don't see Rubio passing up on a popular Governor of one of the most important swing states in the race and a running mate whose long list of accomplishments over three decades in politics can almost immunize him from attacks over experience.
If it's (God forbid) Trump, I have no idea who ends up as the VP pick. It wouldn't surprise me if Kanye West was his running mate.
If it's Cruz, he'll need to recruit someone from one of the more moderate factions of the party to appeal to independents, and it's probably best if that someone's from a swing state. Rubio would be the first person I'd make the offer to, because Rubio's more than conservative enough to keep the base happy while still bringing a surprising amount of appeal to independents given his political leanings. Rubio also can't run for reelection to the Senate at this point, so he might be desperate enough to take it if he really wants to stay in politics. If Rubio shot it down, Kasich would be my next offer. Experienced, accomplished and also from an important swing state, though he's significantly more moderate and may upset some portion of the base. That said, I'm really not sure he would take it either. I think Cruz's only real options are Mike Lee or Jeff Sessions, and I'm not sure either of them bring him any real help in the race. Lee would probably be more palatable to independents and generally does well in favorability ratings, but he's from a deeply red state and doesn't have the appeal to independents of a Rubio or a Kasich. Sessions is in the same boat and doesn't have the favorability ratings.
While we're at this, on the other side of the aisle....
If it's Hillary, the smartest move she could possibly make is to pick up one of the two Castro brothers (the San Antonio ones, not the Havana ones). I'd go for Joaquin, but I'd also take who I could get if I were in her shoes. That said, it's Hillary we're talking about, and she's locked in a showdown for the nomination she didn't really expect. It would not surprise me at all if she made some deal somewhere with someone for a big-time endorsement and gave up her right to choose her own running mate in the process. It could literally be anyone of any significance in Democratic politics.
If it's Bernie, it wouldn't really surprise me to see Elizabeth Warren end up on the ticket, and that would certainly be his smartest move. It would smooth over the ruffled feathers of the party's feminists, who will not be happy over Hillary's loss, it will shore him up against attacks over age and being out of touch and it will attach him to a bright, young, energetic, female senator with a lot of populist appeal that will nicely complement his own. The only drawback is that she, like Bernie, is from a deeply blue New England state, but she might be able to overcome that if she plays on her Oklahoma and Texas roots. If it's not Warren, he might do well to pick one of the two Castro brothers, but I suspect Bernie's too ideologically inclined to pick one of the party's more moderate members. But, I don't know who is other options would be.