Final two is never the Bachelorette. It's too odd to have them "sobbing" one minute about losing and then on to being the Bachelorette literally within days (filming for the Bachelorette starts RIGHT AFTER the ATFR for Bachelor). So, within the last 7-9 cycles, Bachelorette has always been number 3 or 4. With the producer saying recently (and publicly) that we might get a Bachelorette of who is not Caucasian I'd give the nod to Caila of the 4 left (assuming she doesn't win). She is 1/2 Filipino, which is as close to "not Caucasian" as you get with what's left. If Caila wins, all bets are off as to which of them goes as Bachelorette...maybe Amanda, as the "mom with kids" seeking daddy and husband is a good story line and has worked in the past.
Becca would never get the nod, even if she were final 4. She's a VIRGIN and we all know she probably wouldn't kiss enough guys, and certainly isn't prepared to go into the "Fantasy Suite" with multiple guys. Make no mistake, they LOVED Kaitlyn Bristow last time. That's the kind they go for. Not the sweet little virginal type.