Liatha
You've got some great ideas here ...
Alessandro Nivola as Vash I think he's a little too old. Vash and Knives both look eternally 18-20 ... it's like casting vampires. I think that Tom Felton (Draco Malfoy in the Harry Potter movies) would be good. He needs to play some heroes before becoming completely typecast. Or he could stick with evil and play Knives.
James McAvoy as WolfwoodI fell in love with James as Leto in "Children of Dune". He can play anything, and he looks a bit like Nicholas.
Leonardo DiCaprio as KnivesI'm inclined to think that his face is too round for Knives, and he's a bit too old.
Emile Hirsch as LegatoHmm. Cute, but not pretty enough. Legato needs to be gorgeous AND scary at the same time.
Rose McGowan as ElendiraElendira should be a tall, pretty, lithe MALE, otherwise the cross-dressing factor is lost. How about David Tennant? (currently Dr. Who) He looked pretty good as a Companion in a BBC skit:
Aki Avni as Livio Mmm ... he's very hot, and his facial shape matches Livio. Good choice.
Kristen Stewart as Meryl Kristen's voice is too low. Meryl has to be hyper with a squeaky voice, like an annoying small dog. Shirley Henderson (Harry Potter's Moaning Myrtle) would be ideal, but at 43 she's really too old.
Helmut Bakaitis as Chapel Good choice, except if they have any fight scenes. He's doesn't strike me as a physical actor.
Christian Bale as MidvalleyOh yeah.
A rebuttle!!! w00t!!!
Tom Felton as Vash or Knives:....Eh....
Well, in some ways, he's certainly got a better "face", as in chin, for either of the parts. He's also at a better age for the part, so there are two things going for him. However, I'm inclined to think that he may not have enough experience for the parts........ And I'm not a fan of Harry Potter, or vampires, so it's hard for me to take him to heart. Also, especially when it comes to comic book characters, it's very hard to exactly translate that role for an actor onto the big screen. And while Vash is certainly forever young, he's also seen multiple lifetime's of violence and struggle, so it makes sense that while he looks very youthful, he needs to act and behave in a way that's older. Couple that with the fact that Nivola is ONLY 36, and that today's computer and make up effects are so good that we can make any person ten years younger, and Nivola may not be too old for the role after all.
Though, I'm sure there's still someone better than both of them.
3nodding James McAvoy as Wolfwood: I haven't seen the movie you mentioned, but McAvoy is easily one of the best new talents in Hollywood. He can act and, thanks to Wanted, makes him an especially good choice for Wolfwood, I feel. However, I know he doesn't look a lot like Wolfwood, but I think it's a matter of him bringing his own look to the character. So thanks.
Leonardo DiCaprio as Knives: I know how you feel. Leonardo DiCaprio kinda just rolled out of my head, because he's been in some incredibly good s**t lately (Blood Diamond, The Departed, Body of Lies). That said, I noticed that his face is kind of to round... But he's got the right eye structure, at least, and he's good for at least in the top ten Knives possibles. Plus, he has star power. And when stars have star power, they help bring in audiences and alleviate some of the film's budget.
Oh, also....... He's ONLY 33!!! That's not too old!!!
Emile Hirsch as Legato: In much the same way that I chose McAvoy as Wolfwood, I chose Hirsch as Legato. And while he may not be HOT enough to be Legato...... Give me a break. As Speed in Speed Racer, he sort of looks like a good Legato candidate, and he did a very, VERY good job as Chris McCandless in Into The Wild. Also, for a 23 year old, he looks old enough to play Legato who, I believe, is in his late twenties, or even early thirties.
Rose McGowan as Elendira: Umm....... Let me offer you my stance on the character's gender.
The Dark Horse translation states that "she's", a transvestite, but apparently, since the Dark Horse translation is horrible, this has made her a transsexual.
So...... My thoughts are that, she's not a "true blue" transsexual. Rather, she is a female who has had her estrogen modified so that she's badass enough to kick a badass like Livio's stubbly a**.
VIVE Rose McGowan. You may recall that she is the one legged girl from Planet Terror, who had a gun glued to her stump, and got super-powers. The character's name in that movie was Cherry..... And Cherry wasn't very nice all the time. In fact, Cherry was sometimes a very, VERY cruel b***h. But she could also be kinda funny. And with zombies, blood, and sex, Planet Terror was a very, VERY weird movie.
Let's see.... Badass, cruel, funny, female, weird..... I'd say that translates really WELL to Elendira.
Aki Avni: Glad you like him.... But I'm not sure if I do. Haven't seen anything he's in, but having looked at the pictures of him on his website, akiavni.com, I have mixed feelings about him as Livio. He's certainly big and buff enough to at least give off some off that menace that radiates off of Livio before he turns to good, but then he's also got a bit of the same look for stubbly, good Livio.
In the end, I know there's gotta be a better actor. Most likely a stunt double or someone of that gigantic size (Livio looks close to 7 feet tall). As a side note, I did look at various football, basketball, and wrestling stars.... But to no avail.
Kristen Stewart as Meryl: I agree that she's not a good Meryl, but disagree about the squeaky voice.
Meryl....... Doesn't......... Have......... A squeaky voice. THAT feature, if of anything, would go to Milly. Meryl, in the manga anyways, which the movie (miniseries?) would be based off of because the manga is SO much better than Trigun the anime, is not the same brassy b***h in the cartoon. Moreover, she is a lot like Vash. Not sure of herself, or sure of how she plains to live the rest of her life. Unlike Vash, she's not afraid of commitment, and so she tags along after Vash. In this way, the character represents the world that tries to catch up with Vash the Stampede, and trys to surmise his "worth" to the planet Tatooine..... I mean Gunsmoke.
As a side note, I feel both she and Vash have feelings for each other, and if there was going to be a film adaptation of Trigun, they would have to have more scenes and a stronger connection together.
Oh and, WHY MOANING MYRTLE??? THE HARRY POTTER MOVIES SUCK!!!! THE BOOKS ARE OKAY, BUT LEAVE IT AT THAT!!!!
Helmut Bakaitus as Chapel: Stunt double milady. Stunt double.
Christian Bale:.........Yeah. Perfect choice, all the way.