Tennant is a former star of TV's "Doctor Who." MacDonald's film credits include "Gosford Park" and "Intermission."
Set on the fictional Scottish island of Hegg, the movie is about an actress attempting to marry her British boyfriend away from the media glare.
The BBC said some of the scenes of the movie co-starring Alice Eve, Michael Urie and Federico Castelluccio have already been shot on the Isle of Man.
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