If it was up to me, I'd have Uma Thurman play the Major. The idea isn't to get a character that looks exactly what's in the anime, but someone who can effectively understand and portray the character.
I might have Keanu Reeves as Togusa. Togusa always seemed like a bland kind of guy who wasn't interested in much of anything other than tracking down criminals the hard way.
I don't know who I would cast for Batou, that's kind of a toughie. I don't know of too many actors who have a huge build and can act effectively. I guess the main thing is that you get a guy who can express unrequited love but also looks like he was in the military before. idk.
I'd have either Patrick Stewart or Ian Holm as the old guy...what's his name...I forget.
Just for kicks, though, I'd do something upsetting to most anime fans and make the sniper a woman. I'm thinking...Allison Mack?