Reeves is taking on the Michael Rennie role as Klaatu, a humanoid alien who arrives on Earth with his indestructible robot Gort. Klaatu's mission is to warn the Earth's leaders that an alien race will annihilate them if they don't make up and play nice.
Connelly will take on the role played by Patricia Neal in the original.
Scott Derrickson ("The Exorcism of Emily Rose") is directing the remake with production beginning in December. The film will hit theaters in December 2008.
Connelly is currently working on the ensemble comedy "He's Just Not That Into You." She can currently be seen in "Reservation Road," if you live in one of the cities the film is showing, while her 2006 credits include "Blood Diamond" and "Little Children."