Taran Killam did not do his own singing; this is confirmed by one of his tweets.

Did Drew Seeley sing in stuck in the suburbs?

Singer and actor Drew Seeley (who had a brief role in the film) sang in place of Killam. Seeley also sang for Zac Efron 2 years later for High School Musical.

How did Cobie Smulders meet Taran Killam?

Their first meeting was in 2005 when Killam shot a pilot titled “Nobody's Watching” with Canadian actor Paul Campbell, who had known Smulders for years as they shared the same agent. Smulders attended the taping of the pilot and soon after began dating Killam.