I see most of Ash's guys to make an appearance at least. Squirtle in my opnion is going to make a filler type entrance due to it actually being somewhere in Kanto. As for others I think it'll go something like this:
Personally i think Squirtle will be used in a later facility, not just a filler episode, after all there are some people (too many to mention) who would be mad if it doesn't.
Battle Pike- I see a three on three or a one on one. Donphan I think is the most likely choice, I see it versus Seviper. Others to consider- Pikachu because it actually hasn't battled yet. Very weird. Torkoal/Cyndaquill, she may have Steelix. Also Totadile maybe to fight a Shuckle.
I think Muk(poison match) will be used along with Donphan, and (assuming a three on three) probably Corphish, i don't see the jouto pokemon other than Donphan and posibly Heracross picking up much heat during this saga unless the writers decide to evolve both Grovyle and Corphish which would result in a trade for the three starters and Noctowl.
Battle Palace- PIKACHU. This facility is all about trust and Ash doesn't trust anyone more than this guy. I'm guessing a two on two. He uses Swellow/Grovyle and it looses so he puts all trust in Pika.
Remember the facilities do not go by the game standards so pikachu won't be heavily relied upon, heck it hasn't even faught in a facility yet.
Battle Tower- I see the reappearance of Glalie here since its been so uber in the past. This feels like a Grovyle match as well. Also I can see Muk or Heracross returning for some tank power.
If it's not a Sceptile by this point i hope Grovyle evolves during this match, Glalie or Heracross would be a good choice, and also Squirtle.
Battle Pyramid- I think Pikachu is definite as well as Grovyle. I do see another Charizard possibility, but think its glory was in the first Ep against Articuno. I also see Swellow or Donphan as the third.
Okay i have say Charizard has a very high possibility for coming back for this match for a couple of reasons.
1.this is probably going to be the toughest of the frontier leaders.
2.Brandon could either have the regi's or three really powerful pokemon which Ash's current line up will not be able to take down with out some back-up
Personally i hope Ash loses the first time and has to come back posibly after the Sevii Islands which he would get Charizard and have it learn Blast Burn return and win with it, Sceptile, and Snorlax.