Of course, Carell has demonstrated an immense talent for doing a wide variety of voices in animated work thoughout his career – from the hyper Hammy in Over the Hedge, to the Mayor in Horton Hears A Who! to Gary in Saturday Night Live’s Ambiguously Gay Duo shorts.
There is a subtle difference between the voices of Gru and Dru, as the latter’s is just slightly higher pitched than the formers — but there is some logic to the idea of twins having similar voices.