First and foremost, I don't know why so many people even consider Pokemon Live to be canon, as it's an American invention (yes, there are ones in Japan, but the one the US got is an American creation). I mean, that's like saying the live-action Dragonball movie is going to be 100 percent faithful to the series. And unless I missed the episode where Goku was in high school, I don't foresee that happening. They do these live shows all the time, and none of them have anything to do with the cartoons. Remember back in the early 90s there was that Ninja Turtles Coming out of Their Shells tour? Anyway, I'm getting too far out there.
Now, if I HAD to come up with a theory on this, then I would say Giovanni is the most likely candidate, as the Anime stands now. That's assuming Ash's father is someone we KNOW, and not just Soonded or Gonnabitit.