By the sound of your description you just gave, it sounds like your previously mentioned green giant cedar would be a good idea . Maybe a cheaper option would be western red cedar, but seed source has to be in consideration for specified hardy genotype.
Something most spruces and pines won't do when the crowns close in and shade is ever present, is create a visual barrier. Their foliage on the the lower branches will be sparse and the screen effect will be gone.
The western red cedar has great shade tolerance and its lower branches will should retain green foliage throughout life. I'm not sure how well the green giant is represented by its parentage. But I did think I've read that it has shade tolerance and retains lower foliage.
Just a thought.
