Assuming it is the same Jun, I think they'll keep his personality the same. I can imagine a similar rivalry to Ash and Morrison in AG; two guys with huge competitive streaks and bundles of energy. That rivalry amused me a lot. I certianly wouldn't mind seeing something similar.
As for his team, I don't think it'll be the same in the game namely because all of his team is owned by somebody else or we have already seen them enough. The only one they could possibly keep the same would be Rapidash.
I personally think he'll become Ash's riavl, but not a recurring one like Paul is. If he were to appear again, it would be at the Sinnoh League. Again, this is similar to Ash and Morrison. I mean, why reveal another key and recurring rival so late on in the anime?
I'm hoping that he's not another child hood friend of Dawn. How about a childhood bully, or something? Or maybe they could downright hate each other for no apparent reason. I think that could be pretty entertaining, actually.
And finally, his role won't be huge. We've pretty much have all the 'cast' for the 'main event'; Ash, Dawn, Brock, Cynthia, Cyrus, Saturn, Mars, Jupiter, Team Galactic, Team Rocket and possibly Paul. I can't see how he could fit in.