Does Summer Wars or Astro Boy use more American's as the voice actors?
Summer Wars:  The film's voice cast includes Ryunosuke Kamiki, Nanami Sakuraba, Mitsuki Tanimura, Sumiko Fuji and Ayumu Saitō. Astro Boy (film):  Freddie Highmore provides the voice of Astro Boy in the film alongside the voices of Kristen Bell, Nathan Lane, Eugene Levy, Matt Lucas, Bill Nighy, Donald Sutherland, Charlize Theron and Nicolas Cage.
Astro Boy