The official Japanese Pokémon website as well as their official Twitter account have announced the voice actors for the upcoming OVA special Pocket Monsters THE ORIGIN (ポケットモンスター THE ORIGIN). Junko Takeuchi (竹内順子) who is best know for her voice acting role as Naruto Uzumaki will voice Red. Katsuji Mori (森功至) will play the role of Professor Okido. Takuya Eguchi (江口拓也) will voice Green while Tomokazu Sugita (杉田智和) will be the voice of Takeshi.

It was also revealed that 5 background music tracks from Pocket Monsters Red and Green have been newly arranged by Pocket Monsters X and Y Sound Director Shota Kageyama (景山将太) for the Pocket Monsters THE ORIGIN OVA. The tracks will be included on the Nintendo 3DS Pokémon X & Y Super Music Collection (ニンテンドー3DS ポケモン Ｘ・Ｙ スーパーミュージックコレクション) CD set which goes on sale November 13th, 2013. The original background music tracks will also be included.

Sources: https://twitter.com/Pokemon_cojp/status/373369545689276416, http://www.pokemon.co.jp/info/2013/08/130812_g01.html and http://www.pokemon.co.jp/info/2013/09/130906_a01.html