The pair played Allie Hamilton and Noah Calhoun in the film, which won Best Kiss at the 2005 MTV Movie Awards.
Aguilera and Rutler met on the set of "Burlesque" in 2010, and got engaged in February 2014.
The couple share 16-month-old daughter Summer Rain Rutler, and the singer is also mother to 7-year-old son Max Liron Bratman with ex-husband Jordan Bratman.
"I am not in a rush to set a [wedding] date," the star told People in February. "Our love is secure enough that we don't need a wedding to prove our love and commitment. We are enjoying our daughter, our family and our work for now."
"Watching them grow is an incredible thing," she added of her children. "I try to remember to cherish every moment, because I know it won't last forever ... It's a beautiful thing to experience them evolve into the people they become and wonder what they will offer the world one day."
"The Notebook" earned $115 million at the box office, and is being adapted for TV at The CW.
McAdams' audition tape for the film circulated on the movie's 10th anniversary in 2014, prompting director Nick Cassavetes to reveal Gosling initially wanted the actress fired.
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