It’s not as if Michael Cera can’t lie — in character, at least. For three seasons on Fox’s “Arrested Development,” he concealed his more-than-familial fondness for his first cousin Maeby.

But as an actor, the 19-year-old Cera is as guileless as they come, a key reason his profile is rising.

“The guy’s incapable of having a false moment,” says Jason Reitman, director of “Juno,” in which Cera plays a teen father-to-be.

Cera almost seems too unassuming to break out big, but talent is triumphing over modesty.

“Michael is singular,” says “Superbad” director Greg Mottola. “His rhythms, his sense of humor are unlike anyone I’ve known. There’s an enormous sweetness to Michael, but it’s counterbalanced by terror and revulsion. So there’s tension to his performance, which is always more interesting.”

In “Juno,” Cera brings that vulnerability to a surprise pregnancy. Reitman believes one underappreciated aspect of Cera’s ability is that unlike other actors whose ad libs go three times as long as the original line, Cera’s unscripted moments often make the lines shorter and the script tighter.

“It’s as much about pauses and strange emphasis on certain words as it is about changing the lines,” Mottola adds.

Cera’s “Clark and Michael” Internet comedy series, which he co-created with friend Clark Duke, not only shows Cera can play egocentric, it also hints at ambitions beyond acting for Cera. (“Mike is too smart to waste the rest of his life working for people like me,” Mottola says.)

In the meantime, Reitman wonders if he’ll ever see Cera’s darker side. “What I’d give to see Michael Cera actually upset at someone,” he jokes.

Says Mottola: “I predict that the Michael Cera tabloid story will be that he is missing in Canada, that he’s gone ‘Into the Wild’ — but in Mike’s case it will mean he went camping and forgot to tell his manager.”

Recent breakthrough: Co-starring role in hit “Superbad,” which passed $100 million in domestic gross in September.

What’s next: Toronto favorite “Juno” arrives in December, after which Cera will appear in “Youth in Revolt” for Dimension.