In my search for a perfect version of Thomas The Tank Engine & Friends/The Railway Series, I have thought about making Henry the Green Engine and Percy the Small Engine out to be female engines. To tell you the truth, I had always head-canoned them as female since I was a wee lad because I thought the color green was a very feminine color representing Mother Nature. Duck and Oliver being the balance, I never really bought into Henry and Percy as being male.
For Percy, there's a little bit of logic that I'm getting at. Since one of now her prototypes was named Trojan, Percy is short for Persephone - Hades' wife from classic Greek Mythology, which Sir Topham Hatt (the Fat Controller) would give to the engine before bringing her to Sodor. What do you think, guys?
Based on the strength of her performances as Bulma Briefs in Dragon Ball Z/Super and as Minamo "Nyamo" Kurosawa in Azumanga Daioh, I would like Monica Rial to voice Henry.
As for Percy, there's already one candidate I have in mind based on her performance as the Cloverway-era Sailor Moon - Linda Ballantyne.
Oh, then I would like to break it down by voice-acting talent pools.
Henry - Kath Soucie
Percy - Candi Milo
TEXAS (Dallas & Houston)
Henry - Monica Rial
Percy - Tiffany Grant
Henry - Nicole Oliver
Percy - Linda Ballantyne
My top choices for Henry who don't do anime are... Kath Soucie, Grey DeLisle, Teresa Gallagher, Cree Summer and B.J. Ward.
For Percy, the choices who don't do anime are... Tara Strong, Lauren Tom, Hynden Walch, Kari Wahlgren and Elizabeth Daily.