The Scott Pilgrim anime is quite faithful to the manga. It keeps the key elements and storylines the same. Though there may be a few artistic liberties taken here and there, they don't stray far from the original manga.
In one of his early acting gigs, he was supposed to play a serious part but he couldn't keep a straight face during a very intense scene. His co - actors also started laughing because of his contagious laughter and it ended up being a really funny behind - the - scenes story that added to his reputation as a funny actor.