Actor Christian Bale was in Toronto to promote his latest film Hostiles at the film festival, but it was his heavier frame and bleached eyebrows in preparation for his role as former US Vice President Dick Cheney that grabbed the spotlight.

Bale, 43, said he swore he would not undergo another extreme physical transformation to play a character.

But the lure of playing Cheney in Backseat and some arm-twisting from Oscar-winning filmmaker Adam McKay (The Big Short) persuaded the actor to harness the transformation.

"I don't know why I'm doing that again. I kept on saying I can't do that again, but it's Adam McKay... and the bastard went and wrote a really good script," Bale said.

"I kept on trying to find reasons about how to say no and he always had an answer for me... I eventually went, 'Damn it. He's right. I've got to do it, I've got to do it,'" he added.

Bale is known for physically transforming himself for his roles, losing more than 27 kilograms and foregoing sleep to achieve a skeletal look for 2004's The Machinist before then bulking up to play Batman in Christopher Nolan's Dark Knight trilogy.

The actor told film trade publication Variety that he has "just been eating a lot of pies" to prepare for playing Cheney in Backseat, which will follow the former vice president's influence and impact during his years in President George W. Bush's administration.

The film is also set to star Steve Carrell as Donald Rumsfeld and Sam Rockwell as George W. Bush.

In director Scott Cooper's western period drama Hostiles, Bales plays army captain Joseph J. Blocker, a reluctant escort for a dying Cheyenne war chief returning to his tribal lands.

The actor will also be seen playing wise Bagheera in Andy Serkis's upcoming live-action adaptation of The Jungle Book, alongside Cate Blanchett and Benedict Cumberbatch.

Reuters, Fairfax Media