Fresh from his man-of-the-match display in Wigan's FA Cup triumph at the weekend, the winger is the standout inclusion in Pearce's squad.
"I've made it my business over the last six weeks to have a real good look at Callum," the Under-21 boss, who worked with McManaman at the 2011 Under-20s World Cup in Colombia, said.
"I think he's finding his confidence now, he's been nurtured very well by Wigan.
"He's played so well and the culmination of that was a fantastic game in the final. That will give his self-esteem the world of good.
"We're pleased with his development and that happens with players. He came on the international scene a few years ago at Under-20 level, now he's found form at the right time, just before a major championship.
"I've seen fit to take him, even though he's not played Under-21 football."