Do you happen to know if you are going to be on an A319 or an A320? You can tell from the seat map. None of the 319s have satellite, and 10/53 A320s do.
In any case,
Viasat does not work over Mexico, so you'd only have an hour or less of usable service even if you ended up on one of the planes that have it.
Maybe you get lucky and they swap in an A321 or a 737 with 2Ku at the last minute, but I doubt it.