Sandra Bullock and Keanu Reeves are both such guarded celebrities that I have a hard time imagining them as lovers, a problem this romantic fantasy set in Chicago surmounted by isolating them from each other almost entirely. The engaging script, adapted by David Auburn (Proof) from the South Korean movie Siworae (2000), separates the leads not by distance but by time: living in a picturesque lake house in suburban Willow Springs, Reeves keeps getting notes in his mailbox from Bullock and eventually realizes that she’s living in the same house two years in the future. Teasing out the practical implications of this premise takes up most of the movie, which helps contain a trite subplot about Reeves’s relationship with his famous father (Christopher Plummer) and allows the two stars to luxuriate in their solitude. Alejandro Agresti (Valentin) directed. PG, 98 min.