With a Japanese-strong cast in place including Hiroyuki Sanada as gang boss Shingen, Tao Okamoto as his daughter Mariko, Rila Fukushima as assassin Yukio, Hal Yamanouchi as gangster Yashida, Will Yun Lee as villain Silver Samurai and Brian Tee as a corrupt politician, Biel's athleticism likely made her a top candidate to play Viper. That said, it looks like they'll now have to find someone else to step into the character's boots.
Originally a Captain America antagonist before becoming the presumed lover of Silver Samurai, Viper has no real powers but is best known for her athletic ability and skills in martial arts as a swordswoman and a markswoman. She first comes across Wolverine when thwarted by the clawed anti-hero in trying to poison gang boss daughter Mariko but, in later comics, she became more ambivalent, blackmailing Wolverine into marrying her, and developing real feelings for him.
It'll be interesting to see what direction casting goes in now with the character supposedly of Eastern European descent in the comics. Surely a replacement will be lined up fairly quickly with lensing on "The Wolverine" due to get underway next month as it aims for a July 26th, 2013 release.