They need to leave Aquaman off the team for this in my opinion. I could see them deciding to add Plastic Man to the team for comedy purposes.
My prefered team is as follows
Batman- Token appearence
Superman- Token appearence
Wonder Woman
Green Lantern
Flash
Green Arrow
Zatanna or Black Canary
Martian Manhunter
As to who protrays them is another question. Jessica Beil as WW would work, Ryan Reynolds as the Flash, Eric Bana as GL, for GA get Cary Elwes back into shape (remember Robin Hood: Men in Tights?),and paint Bobby Lashley green and we've got the Martian Manhunter.
Zatanna and Canary are harder to cast. In the comics I have never been able to figure out what nationality Zee is.