Shiloh Fernandez had originally auditioned for the role of Edward Cullen in Twilight (2008) before Robert Pattinson got the role. Catherine Hardwicke remembered that he auditioned and offered him the role of Peter as a way of making it up to him.
Christina Ricci was originally considered for the role of Valerie, and was a strong candidate before Amanda Seyfried was selected. It was decided that she was too old for the role and was several years older than both love interests, Shiloh Fernandez and Max Irons.
Max Irons would go on to star in The Host (2013), which was an adaptation of the Stephanie Meyer novel of the same name. Catherine Hardwicke previously directed Twilight (2008), which was also an adaptation of the Stephanie Meyer novel of the same name.
The trivia items below may give away important plot points.
With the exception of Valerie (Amanda Seyfried), all the characters from Daggerhorn are either played by actors with brown eyes or wearing brown contact lenses. Most notable of the latter is Julie Christie, who plays Valerie's Grandmother, who is famous for her blue eyes. This was to add to the suspense and mystery on who could be the werewolf in hiding, as Valerie saw the werewolf had brown eyes in her encounter with it.