Kurt Cobain - Ryan Gosling
I think that this guy is one of the best actors around and he's incredibly underrated. Nobody pays him much attention, but he's awesome. He's been nominated and won plenty of awards for his extraordinary acting talent. He's also a pretty good singer, has experience with drug related roles and physically fits the role somewhat, just some new hair and makeup would do the trick.
Roles - The Notebook, Half Nelson, Blue Valentine
Krist Novoselic - Matthew Lewis
I really enjoy watching this guy, especially in the Harry Potter series. He's got some great talent and can really have a good future in film. Also, he looks exactly like Krist!
Roles - Harry Potter 1-8, The Sweet Shop
David Grohl - John Robinson
Although I don't get to see him in much, I think he's a pretty good actor. Has some talent that he can use in this role. Physically fits the role somewhat, just some new hair and makeup would do the trick.
Roles - Lords of Dogtown, Elephant, Transformers
Courtney Love - Rooney Mara
I think this girl could be an upcoming star. She's already won some awards for her performances and I think more can come. She's very pretty and I think using acting and makeup, she can portray the perfect Courtney Love, a pretty girl ruined by her reputation and drug addiction. Physically fits the role somewhat, just some new hair and makeup would do the trick.
Roles - The Social Network, The Girl with the Dragon Tattoo, A Nightmare on Elm Street