The Torchwood actress has had multiple call-backs during the audition process and is a strong contender to play the DC Comics heroine, STV claims.
Amazon has been compared to Superman-themed show Smallville and will reportedly bear no resemblance to David E Kelley's recently rejected Wonder Woman pilot.
CW president Mark Pedowitz previously confirmed that the series will not show the protagonist in her Wonder Woman costume, at least initially.
In addition to her role in Torchwood, Scottish-born Manson has appeared in BBC supernatural drama Being Human.
A script for Amazon is currently in development with a shooting schedule yet to be confirmed.