As much as I would want the DCCU to include Arrow universe but to be honest, the chances are slim. So this is my fan-cast for the extended universe of ARROW and FLASH with characters related to BATMAN stories. Some of these are already in the tv series ARROW.
Jim Caviezel as Batman
Peter Capaldi as Alfred Pennyworth
Brett Cullen as Comissioner James Gordon
Giancarlo Esposito as Lucius Fox
Nathaniel Buzolic as Nightwing(Dick Grayson)
Alexandra Daddario as Batgirl(Barbara Gordon)
Steven R. McQueen as Red Hood(Jason Todd)[my choice for him as Jason while it looks like ARROW crew may have something else in mind]
Dylan O'Brien as Red Robin(Tim Drake)
Sarah Clarke as Batwoman(Kate Kane)
Lyndsy Fonseca as Flamebird(Bette Kane)
Amy Acker as Talia al Ghul
Esme Bianco as Catwoman(Selina Kyle)
Jessica de Gouw as Huntress(Helena Bertinelli)
Gage Golightly as Spoiler(Stephanie Brown)
Madison McLaughlin as Black Bat(Cassandra Cain)
Chandler Riggs as Robin(Damian Wayne)
Gustaf Skarsgård as The Joker
David Dawson as The Riddler
Gideon Emery as Two-Face
Mads Mikkelsen as Black Mask
Conleth Hill as The Penguin
Alexander Siddig as Ra's al Ghul
Jonathan Tucker as Scarecrow
Todd Williams as Morgan Ducard
Cara Delvingne(my own choice) or Cassidy Alexa(looks like they have already chosen) as Harley Quinn
Kevin McKidd as Bane
Gregory Itzin as Hugo Strange
Sean Bean as David Cain
Hugh Dillon as Mr. Freeze
Scott Adkins as Talon(William Cobb)
Manu Bennett as Deathstroke
Mark Pellegrino as Catman
Travis Fimmel as Owlman
Maggie Q as Lady Shiva
Daniel Sunjata as Electrocutioner
Michael Rowe as Deadshot
Sebastian Roche as Cluemaster
Robert Knepper as Clock King
John Barrowman as Merlyn