Variety.com said Penn has signed up for the role of Larry, while Carrey is in talks to play Curly and MGM is courting Del Toro to play Moe.
The entertainment industry trade newspaper said the movie won't be a bio-picture but a comedy about the antics of the three characters that Moe Howard, Larry Fine and Jerome "Curly" Howard started playing in the 1930s.
Peter and Bobby Farrelly co-wrote the "Stooges" screenplay and are producing the movie, which is to go into production in early fall for a 2010 release, Variety.com said.
The film marks double Oscar winner Penn's first comedy since 1989's "We're No Angels."
Del Toro was recently seen in "Che" and Carrey in "Yes Man."
The Farrelly brothers' films include "Dumb and Dumber" and "Me, Myself & Irene," both starring Carrey, as well as "There's Something About Mary" and "Stuck on You."