No one reads the explanations, so I kept it short. Enjoy and please leave your comments, good and/or bad.
Cable/Stryfe - Gerad Butler
Cable is a fan favorite, no introduction needed. Butler has everything you want to bring Cable to the big screen.
Cannonball - Josh Hutcherson
Josh isn't known for much outside of the Hunger Game series where he has really shines and should earn some really good roles. Cannonball is a leader in every facet first as a New Mutant then X Force then as an X-Men. As Cannonball I know he brings what's needed to the fiery rebel leader.
Moonstar - Seychelle Gabriel
Moonstar was an original New Mutant who posses the ability to create images of fear and desire from her opponents into realistic images. Seychelle Gabriel has done some voice work (Legends of Korra) and actually played in The Last Air Bender as the Ice Princess. She was convincing as a sexy, street savvy, loud mouth dancer on Honey 2. She has potential and should do Moonstar some justice.
Sunspot - Jake T. Austin
Sunspot is fantastic mutant he absorbs solar energy and radiation which turns his body into darkness. He can shoot solar blasts from his hand and he can fly among other abilities. Jake T. Austin has the look and savvy attitude to portray the cocky mutant. He's a young talented actor who could bring out best in Sunspot
Karma - Malese Jow
She has a decent resume espiecial with WB. She's been in Flash, Star-crosssd, and Vampire Diaries. In each show she's brought something different. Karma is a mutant that possesses the ability to take control over another person and had a cool cybernetic leg to boot (pun intended.
Wolfbane - Maisie Williams
Another original New Mutant. Wolfshone comes from Scotland abandoned by a priest father after a failed exorcism she was a loner at 14 when her powers manifested. She is like a werewolf in the the since that she can transform to and from her wolf form or hybrid wolf. She can heal, she has enhanced speed, agility, and she's telepathically linked to Moonstar. She's fantastic in GoT and her acting would do wonders for this role.
Domino - Kristen Stewart
Kristen Stewart Yes I know she is dull and twilight was a staple for her. But the girl can act and I think she could play the tough girls really well. She has the look to play Domino. Domino is a mutant that has the ability to change things in her favor, plus she's extremely gifted with weapons and in martial arts. I'm gonna get backlash, but she's more than capable.
Magik - Chloe Grave Mortez
She can kick butt (pun intended) she's a really really solid actress. She has the attitude to play the tough girl role, but also has just enough femininity to play the girly girl. I see her bringing out the best in sword carrying New Mutant.
Warpath - Avan Jogia
I know Booboo Stewart, but they recanted Colossus so yeah I'm recasting Warpath. Avan would do well in this role.
Magma - Rosie Huntington-Whiteley
Joined the mutants for a short period of time before leaving for the Hellions. She transforms into well magma and has the ability to manipulate the Earth. Rosie Huntington-Whiteley is a young up and coming actress and after seeing her in Mad Max I'm convinced she can do some more action films. Magma perfect for her, they are perfect from one another.
I was going to add kore mutants like Surge, Waliflower, Elixir etc but I will do another fan cast later.