I found some interesting stuff about Unnatural & Accidental
here.
From the director's notes:
Perhaps the most difficult actor challenge was casting the central antagonist ..Norman... This is not a very nice role, and I could not think of too many actors who would be willing or even capable of playing the necessary darkness that this character demands. Of all the Canadian actors I know, Callum Keith Rennie was the man whose body of work showed the most promise in this role, but even Callum was reluctant to play such a dark character. After lengthy discussions, and a period of time where both of us were given an opportunity to express our thoughts about the script, the approach to the role, the way in which we would shoot the more difficult scenes, Callum came on board. When I look at the finished film, I am so relieved that Callum agreed to play this role. His deep understanding of the darkness that motivates ..Norman.. gives every scene in the film enormous credibility.
So, um. Of "all the Canadian actors" Carl Bessai knows, Callum's body of work showed the most promise for playing... a serial killer without any redeeming qualities? I... just... *sigh*