The acclaimed writer initially identified Ryan Reynolds as his first choice for the part of Johnny Bolt in Nacho Vigalondo's upcoming film.
"Ryan Reynolds should play johnny bolt in our Supercrooks movie. He'd be perfect for it. Such a likeable actor," he wrote on Twitter.
However, he later agreed that Hangover star Bradley Cooper would be a good fit for the role after a fan made the suggestion.
"Good call. Bradley cooper would be an amazing Johnny Bolt. Nacho, we should write that down," he said.
Supercrooks, written by Millar and illustrated by Leinil Yu, tells the story of a group of supervillains who move to Tenerife in the hope of finding an easier environment in which to perpetrate their crimes.
Vigalondo's movie adaptation is scheduled for release in 2014.