The film had its world premiere in Toronto. The epic love story, set in the present day and World War II, is about an American woman who looks back on a wartime promise.
Shirley MacLaine, Brenda Fricker, Christopher Plummer, Mischa Barton, Neve Campbell and Pete Postlethwaite star.
Financiers are Bank of Ireland, the UKFC, SCION, NFTC and ContentFilm.
Attenborough also produced alongside Jo Gilbert. Martin Katz co-produced.
ContentFilm said the rights were almost sold out, with deals already struck for the UK (The Works), Spain (Manga), Japan (Shochiku), Germany (Telemunchen), Australia (Hopscotch), the Netherlands (A-Film), and Canada (Odeon).
Barry Gordon, executive vice president of home entertainment, negotiated the deal on behalf of The Weinstein Company with ContentFilm's Jamie Carmichael.
The film has now almost completely sold out, including to The Works in the UK, Manga in Spain, Shochiku in Japan, Telemunchen in Germany, Hopscotch in Australia, A-Film in the Netherlands, Odeon in Canada.