Also because the scale is so hard to see, the porch is 7.5 feet deep (front to back) and about 23 feet wide (left to right). The roof is ten feet from the floor at the lowest. The door is absolutely massive- I think ten feet tall. Which is why I'm looking for a big filler.

If I planted anything like that in black, be it plastic or metals (worse yet) it'd be a gone-er! I'd think you would've planted coneflowers or phlox paniculata....
Or some sort of muhely or pennisetum type of grass, that has long flowering stems, but not sure of temps, although you mention 4 hours sun exposure, high summer, currently passed just two weeks ago, so I'd expect more sunlight hours and warmth, the duration of, or for the rest of summer..
But also, a little bit of something similar to ivy, or potato vine, that drapes or trails downward, so it doesn't look quite as barren,, for the extreme height of the pot..
Maybe even type 2 Clematis and cut it back, once in spring & again after flowering once again, in autumn.

I have spirea growing in a large container on my east-west oriented breezeway. It gets bright shade plus an hour or so of sun. It's not under the breezeway roof so it also gets whatever moisture Mother Nature doles out (which has been a generous measure this year). It has come through the past two winters and it bloomed this year. NB - I grew it from seed via winter sowing so it's naturally more robust than a nursery-grown plant.

Nice porch! Love that natural stone and huge door, very nice.

I used to do shrubs in containers all the time, and it works great. However, they won't be able to overwinter in a pot, most likely. In the fall you can pull it out of the pot and put in in the ground temporarily, then re-pot it in the spring. But sometimes that fails too, so I have come to view shrubs in pots as temporary fixtures. That said, they don't cost anymore than a pot full of annuals so why not?

As for what shrub to choose for that spot, if I were to toss out one idea it would be Ivory Halo dogwood, which takes shade and is a beautiful plant, year-round. It's very hardy too. It does not like to be dry though, so attentive watering would be important.

I am looking at the space in your photo and thinking that you don't want to crowd the door (feels unfriendly) and you don't want to block the window, so you really want something tall and relatively narrow, perhaps a vine for shade on a trellis, and maybe including some draping plants as well. I can't think of any narrow shrubs for shade, particularly ones that will overwinter in the pot for you (zone 3b hardy.)

If you want some inspiration for annual shade plantings, I've included a link to a Detroit area designer who I think does beautiful work. If you decide to go the annuals route, she also does stunning winter containers, and you could do seasonal arrangements.
Here's some inspiration for winter containers.
http://www.deborahsilver.com/blog/?s=container+winter

You can also look at her placement of containers to see if any other spots might work visually but give you more options for planting.

Here is a link that might be useful: Deborah Silver shade containers

Babs, I love that site!! Thank you! I think you're right re: tall and skinny. Will post another picture tomorrow of the containers.

I'm thinking tall and skinny as well. My first thought was that while tall and skinny works for the placement of the pots, it wouldn't work in those tall narrow urns, making it TOO tall and skinny and bottom-empty to boot. But now, in looking again and again at your photo, I'm rethinking that. Perhaps these pots will complement and enhance the tall and skinny look.

My first thought was ilex sky pencil. I'm not a great admirer of its form, but it does work well for these types of spots, and I believe it would be hardy and do well in the light conditions as well. You would have to double check the hardiness as I don't recall the exact zone off the top of my head. I think it calls for full sun but I grew one in part sun (in a pot) and it did fairly well. I ended up giving it away when I found something better for the spot.

I'm also thinking of ilex Castle Wall and/or Spire, which I think are more pyramidal. Not sure again exactly of zone or conditions, or even if this is "skinny" enough, but just going off the top of my head here.

Maybe ilex Earlibright? Again, sorry, not sure of zone, but I think this is a fairly narrow, upright form and would give great winter interest (if you have a pollinator nearby).

I seem to have ilex on the brain today, lol.

As a person who is terrified of pruning, I don't know if any of these would be amenable to pruning for size. I would think the Sky Pencil and Castle Wall would be, but not sure about the Earlibright.

And this may all be for nought if the zones aren't right....

Oh, one last thought - yucca? Golden Sword is quite nice, and while in bloom would give you the height you are looking for. And I think it is zone-4 hardy, so might work for you over winter as well. Not sure about sun exposure. I did grow these in pots on my back patio for winter interest, and they looked great over the winter, but died on me in spring from some kind of (I think) fungal thing.

Please let us know what you decide. This is kind of a challenge, in terms of perennials!

Dee