Young Knives is voiced by Joshua Seth, voice of Tai from Digimon Adventure. It's very easy to tell, seeing as how he does nothing to differentiate Young Knives from his Tai voice. One could put a voice clip of Young Knives onto Tai and Digimon fans who haven't seen Trigun would be confused.
Rem is voiced by veteran voice actors on both sides of the Pacific.
In English, she's voiced by Bridget Hoffman, voice of Namie from Durarara!!. Now, try to imagine her suddenly as a mother figure to Izaya. For what it's worth, Hoffman also played Belldandy in the Ah! My Goddess movie (and has dubbed at least three other roles originated by Kikuko Inoue).
The Other Darrin: The only voice actor to return to reprise their role for the movie's English dub is Johnny Yong Bosch as Vash. Jeff Nimoy and Dorothy Fahn were both interested in reprising their roles of Wolfwood and Meryl respectively, but Funimation replaced them behind their backs mid-negotiations. Lia Sargent was also replaced as Milly, but this was expected as she had retired years earlier.
What Could Have Been: Much like InuYasha, Trigun was one of the [adult swim] anime shows that was meant for Cartoon Network's Toonami block, but ended up airing on [adult swim] instead due to content issues (in this case, it was due to the amount of gun violence that would have to have been edited down... and a few scenes got censored on [as] anyway)note The most notable cut made in the Adult Swim airing was in Episode 7, where Brilliant Dynamites Neon shoves his gun in Kaite's mouth and keeps it there for nearly 30 seconds.
Oddly enough, Trigun, along with the original 1963 Astro Boy, was showcased during the April Fools Day 2012 Toonami broadcast, despite the two not having aired on Toonami before.
Ever since Toonami was revived on [adult swim] hours, Trigun now has a chance to make an official premiere on Toonami (again, much like InuYasha before it). So far, however, it has yet to do so. Though considering Badlands Rumble was picked for their December movie marathon...
Word of God: Nightow says that Kuroneko-sama is female and that Vash and Wolfwood aren't in a gay relationship, yaoi Doujinshi notwithstanding. He has also provided Wolfwood with about half a dozen middle names to go with that 'D.'
The best obviously being Dokonokuminomonjawaresumakinishiteshizumetarokakora.