Because Exotica was a small Canadian film, there was very little in the press about the casting of the movie at the actual time decisions were being made. There were a few famous statements made by Atom Egoyan later on how Bruce Greenwood was selected and those are included here:

Pevere: A really unusual choice, it strikes me, for Exotica was Bruce Greenwood, a Canadian actor best known for work on American TV. How did you settle on him for Francis?
Egoyan: An odd way. At one point I was thinking -- and you can't think of someone more completely different from Bruce than Maury Chaykin -- but Maury was one of the people I was thinking of for Francis.
Pevere: That sure would have been a different film.
Egoyan: Totally different. But the schedule with Maury didn't work out so Maury's agent, Debbie Peck, suggested Bruce, and I owe a lot to her. At the moment I saw Bruce's work I thought he'd be perfect, because I love the idea of a man being found in a club like that whom you wouldn't think would need to be there. It immediately makes you wonder why he's been brought there.
An Interview with Atom Egoyan by Geoff Pevere, 1/16/95

By April, Egoyan was already seeking talent for the leading roles. After a number of changes to the character of Francis, Egoyan focused on noted Canadian actor Bruce Greenwood. At the time Greenwood was in Toronto filming Women on Trial. After discussing the role and the film, Greenwood was immediately fascinated by the character and Egoyan himself. "I wanted to do something that would resonate longer. With Atom's work I realised that the closer you look, the more there is to discover," Greenwood later explained. Once he was back in LA, he continued to discuss the role of Francis with Egoyan. Francis is a complete, multi-layered character who, according to Greenwood, "has had his ideal for love and of family removed forcibly from him. Francis has wandered into an abyss, prompted by the betrayals he has endured which have taken away his equipment to deal with reality, so he creates his own reality."
Exotica Production Notes, Lumiere Cinemas

Greenwood is best known for his role as Set Griffin on "St. Elsewhere," and Egoyan cast him against type. "He always plays golden boys, but he's a really talented actor, and he isn't seen doing that sort of role. I thought, 'Why don't we take this very handsome man and make him look as run down as possible?' You know by looking at him that he's let himself go."