Hugo Weaving for Runge?

Fantastic suggestion - he has the same sharp facial features and he is an incredible actor. I think he could pull it off assuming he is not too short or skinny. Lunge seems tall and broad to me.

Here are some of my suggestions that I think are spot on:

Tenma - Hiroyuki Sanada
http://www.imdb.com/name/nm0760796/?ref_=tt_cl_t6
http://thefilmstage.com/wp-content/uploads/2012/04/hiroyuki-sanada-lead.jpg

This guy is a great actor that has Tenma's low-key yet dramatic persona down pat.

Roberto - Peter Stormare
http://www.imdb.com/name/nm0001780/
http://www.989thedrive.com/thedrive/wp-content/peter-stormare.jpg

This guy can do anything - he already has the look and accent. This guy has the chops to take Roberto's character to another level.

I would have liked to see Michael Shannon myself. He basically plays the same dude in Boardwalk Empire.