According to the DVD extras, Julie Andrews was chosen as Mrs. Gru specifically because, of all well-known actresses, she was the least suitable person to play an evil old woman — so choosing her to do so invoked the Rule of Funny. (She refused the part at first, but was persuaded.)
Mexican moviegoers may notice that the Latin American Gru sounds just like Mike Wozowski with an accent. Or Dr. Chunga.
Spanish moviegoers can see how Florentino Fernández is the voice for both Gru and his mother and the beautiful Ana de Armas (El Internado) plays Margo. You can even notice the accent Ana uses (in an interview she stated how hard it was to say "cisnes" (The Swan Lake is translated as El lago de los cisnes) correctly, because she would normally pronounce the 'c' as an 's').
The man working the carnival game (Aww, somebody's got a frowny face!) is Phineas and Ferb's number-one fan, Irving. Once you hear his voice again, it's pretty easy to connect.