Here is who I will cast for uncasted characters of the Marvel Cinematic Universe I will also add what films should be in the untitled Phase 3 Marvel movies and Phase 4. I will also be adding X Men and fantastic Four if Fox want to share them with Marvel.
Untitiled Phase 3 Marvel Movies
Fantastic Four and the Inhumans
Black Widow
Phase 4
Fantastic Four: the Incursion of the Skrulls
X Men Phoenix
Spiderman 2
Spiderman Movies
James Nesbitt as Norman Osborn/ Green Goblin- Watch James Nesbitt as Jekyll in the 2007 BBC drama Jekyll and you will see why he is the definate Green Goblin
Steve Pemberton as Otto Octavius/ Dr Octopus
Mark Gatiss as Curt Conners/ The Lizard
Captain Marvel
Hannah Spearitt as Captain Marvel/ Carol Danvers
Avengers: Infinity War
Aiden Turner as James Logan Hewlett/ Wolverine
Fantastic Four and the Inhumans- This film would be the origin story of the Fantastic Four in the MCU. This version of the Fantastic Four will be Inhumans and the cosmic ray that they were exposed to to get their powers in the MCU is terrigan and then their spaceship will crash in Attilan after exposure. The MCU Fantastic Four will be Marvel Doctor Who.
Matt Smith as Reed Richards/ Mr Fantastic
Lily James as Sue Storm/ Invisible Woman
Robert Kazinsky as Ben Grimm/ The Thing
Bradley James as Johnny Storm/ Human Torch
Kara Tointon as Medusa
Hannah Tointon as Crystal
Black Widow
John Simm as Wade Wilson/ Deadpool- I think Deadpool would be a very good comic relief character in a Black Widow Solo movie if Fox Shares him with Marvel.
Adam Driver as Victor Von Doom- This will be Dr Dooms first appearance in the MCU, He is not yet the Doctor Doom we know in the comic. in this film, he is a Jihad John style terrorist working for A.I.M and Hydra who threatens to release a deadly leprosy like disease. In the end of the film he is affected by the disease losing his limbs, disfiguring his face, then he is saved by Hydra and restored using Iron Man/ Ultron/ Chitauri technology and becomes the Doctor Doom that we Know and love. He will not return until the beginning of Phase 5.
X Men
Timothy Dalton as Charles Xavier/ Professor X
Arthur Darvill as Cyclops/ Scott Summers
Amy Manson as Jean Grey/ Phoenix
Freema Agyeman as Ororo Munroe/ Storm
Stephen Fry as Hank McCoy/ Beast
Rachel Stevens as Allison Grimm/ Dazzler- This version of Dazzler will be a cousin of Ben Grimm/ the Thing
Lacey Turner as Kitty Pryde
Derek Jacobi as Magneto
Anthony Head as Nathaniel Richards/ Mr Sinister
Dave Schneider as Nightcrawler
Marc Warren as Sabretooth