HP 757's some are ETOPS (Extended Operations) and one or two are simply EOW (extended overwater). The EOW a/c (914) can be used for Cancun, but not on distances without a suitable airport to land at within 180 minutes ie, Hawaii). Its complicated. There are no ETOPS nor EOW airbus a/c in the hp fleet. I imagine, that if there is an available East EOW airbus a/c in PHX to operate PHX-CUN during low season (now), they would use it. First, because it's available, second, because it's a smaller a/c during season with less demand. third, because it can shave off some flight time saving in fuel versus the HP airbus which would fly the original 4:45 block time or so hugging the Mexican coastline.