I have read that ERC grows all the way up to the Canadian border. If the tree is over 50 ft. tall, it's not ERC. Northern white cedar does not have the little light blue berries. Atlantic white cedar is less likely since it is more coastal, but it does have blue berries. They are darker and less smoothly round than ERC berries.
This is all from Golden Field Guides "Trees of North America". Hope it helps.
Mike