Here's a list of some plants that will grow in Zone 4.

Creeping Cotoneaster
Alpine Aster (Aster alpinus)
Snapdragon (Antirrhinum majus 'Sonnet')
English Oak (Quercus robur)
Bee Balm (Monarda didyma 'Marshall's Delight')
Oxeye (Heliopsis)
River Heritage Birch (Betula nigra 'Heritage')
Sugar maple (Acer saccharum)