arbor vitae hedge
Attached is a list of some recommended plants that are evergreen and maximum 4-feet tall. This list was produced using our Plant Elements of Design plant selection program: http://landscapeplants.extension.umn.edu/ This is a free program that requires only a user name (email) and password. It contains over 2800 plants and about 5000 images of plants that are good options for upper Midwestern landscapes. For more information http://www.extension.umn.edu/garden/landscaping/plant/
Another list of broadleaf evergreens for zone 4 can be found here in the attached PDF from our online book, The Best Plants for 30 Tough Sites.