There are currently two Marilyn Monroe biopics in the works. The first one, My Week With Marilyn, had already been announced, and has Michelle Williams in the lead (taking over for Scarlett Johansson). That film is based on a diary by Colin Clark, who worked for Laurence Olivier while he escorted Monroe around London while filming The Prince and the Showgirl. That Weinstein production, set to begin shooting this fall, will be directed by Simon Curtis.
Meanwhile, the just announced Marilyn biopic, Blonde, will feature Naomi Watts in the lead role. That one is based on the fake memoir by Joyce Carol Oates, which is the “story of Norma Jean as a central figure in a fairytale; an orphan child lost in the woods of Hollywood, being consumed by that great icon of the twentieth century.” That one will be directed by Andrew Dominick.
The Naomi Watts version sounds like the more interesting of the two, but I give the narrow edge to Michelle Williams as the better potential Marilyn Monroe.