Most likely Alain has a Pokemon of each region that is already been showcased in the anime. I can see him with a Dragalge for gen 6. Main reason is, that the other game-exclusive Kalos mons already have been showcased in battle (Clawitzer with Shota, Slurpuff with Shota and Miette and Aromatisse with Aria). And i can see him having a Swanna. Main reason i can think of is an aerial battle against Talonflame. Since it looks we get Salamence vs Noivern, while Talonflame took on a floater, Clawitzer. They can reverse both. Salamence is effective against Noivern, while Noivern is affective against Salamence. Clawitzer was effective against Talonflame, while Talonflame wasn't effective against Clawitzer. Talonflame was taken down by a floater. They can Noivern take down Salamence against Shota, but losing against the Dragalge, a floater and let Talonflame win his aerial battle.
I can also see they matchup Hawlucha vs Metagross and let Hawlucha take down Metagross, which he couldn't do against the Slaking, despite being Super Effective. Then Goodra vs Tyranitar (First matchup) and Pikachu vs Weavile (Second matchup, when Weavile has taken down Goodra). Then Pikachu gets recalled. I can imagne Ash three strongest (And the ones that have been on his Kalos team the longest), are going to match up against Zard X (Pikachu, Talonflame and Ash-Greninja, in that order, with Talonflame damaging Zard X, like it did with Mega Lucario so Pikachu could take it down).