Maggie Gyllenhaal is starting to make a career out of replacing actresses'. We already know that she swooped in to replace Katie Holmes in The Dark Knight for the boring role of Rachel Dawes and Variety report today that she has done it again with Sam Mendes' upcoming and still untitled comedy. She will replace Toni Collette (who dropped out for scheduling clashes) as the College Prof. who has a history with lead John Krasinski. The comedy revolves around a road trip between Krasinski and his new wife played by Maya Rudolph, who are searching the U.S. for a place to settle and start a family. Gyllenhaal will begin filming her part next week. Mendes next movie and his fourth completely different genre in as many films - Revolutionary Road which reunites Titanic pair Leonardo DiCaprio and Kate Winslet for the first time since that ship a decade ago, will be released at Christmas.