Chris Evans does his own singing in the movie.
Behind the scenes, Anna Faris was in a hard spat with the producers, because she disagreed with the outfit of her character, especially the slender or very narrow high heeled shoes.
By the time the film was greenlit, the script was a few years old. Anna Faris was adamant that they raise Ally's number of sexual partners, because she felt that a girl her age in the modern world would have more life experience. The studio, on the other hand, was adamant that it be 16 partners because they felt too many partners would make the character unrelatable to the audience. Faris lost the argument and the number they settled on was 20 sexual partners for Ally.