A great tree for this purpose would be the Canadian Hemlock. As an evergreen hemlocks will provide privacy year round and can handle the cold of zone 3. Naturally they’ll follow their instinct and try to grow into a tree but pruning the top will force it to branch out and go wide instead of tall. Gradually let it get to the height you want and then trim the top every other year or so to keep it low and bushy. Hemlocks are widely available.