I recently read the Jessica Beil was asked about portraying Diana in a future Wonder Woman movie. This movie has been talked about since the late 70s and early 80s. In recent comic book issues and animated films there has been considerable resources into updating this character. If you have not seen the recent animated film by DC Comics, I would suggest watching it. I think it was a good movie. It really set the stage for future projects.
As a fan of the series since the mid 70's, I feel that this will be the hardest character to bring to a live action movie. Diana is a very complex character with many layers. The character has a long history, which is well documented. As the director, Lauren Montgomery discovered that it was not possible to make a origin film that someone found a problem with.
I like the origin the was setup in the new animated series. However, I would have changed, Steve Trevors character to be more like James Bond like. I would keep the "intelligence agent" aspect of the story. However, i would bring the other Amazons into the story. They should have a team of amazons like the quartermaster(Q) branch of MI-6 in James Bond.
Diana should realy be agent for Themyscira, and Steve should be her American liason. They should set up a embassy in Boston, where Diana gets her assignments and can talk with the Queen more.
I think the actress best for the role of Diana is Kate Beckinsale. She is perfect for the role, and she is a "A" list actress. I think the person best to play Steve Trevor is Brad Pitt. To make a movie work the dynamic between Diana and Steve is necessary to drive the film.
My pick for Etta Candy would be someone like Lea Remini.
If she is to old, Amanda Bynes would be perfect.
My choice for Artemis would be Katee Sackoff.
My choice for the Queen would be Jacqueline Bisset.
Erica Durance would be good for the role or Steve Trevors daughter or Julie Kapatelis. Although, I think Erica would be better as Barbara Minerva.
If they decide to cast Linda Carter as a tribute, she would be perfect for the lady who Diana rents an apartment from, Camille Sly.