Ok this seems a little wierd, why the hell couldnt Keanu Reeves just play both Freck and Arctor? They are the same freaking person! Although Arctor is Freck in a scramble suit... he is still Freck. There is no reason at all to confuse the audience by slapping them in the face with a different actor for both Freck and Arctor.
This is a very dangerous tactic seeing as you dont really catch on to who is too quickly even in the book, only when he tries to get his fix do you realize that the man behind the static is infact Feck. So, in my opinion, making two people play what is essentially one man will just throw off people who have never read the book!