I am on the west coast of Canada, and am very familiar with, and have snipped all sorts of crazy things out of Western Red Cedar, Thuja Plicata. Are we talking about the same tree?
If so let me know and we'll go from there.

This is Eastern Red Cedar, juniperus virginiana. Lives about 300 years, can get 120 feet tall. "though from what I've seen, not here in central Oklahoma> It's the other key species in the Cedar Apple rust loop, and self sows so readilly it's considered a pest, it's not a true cedar, but it is a dense evergreen.

Our place is full of them, most are narrow columns that look like they just need a little trimming to square off the tops and sides and I would have a field of box trees. (or triangles, or poodles, or whatever.) Not sure I can do a wedding cake with them, but I think I could work out a spiral which would look terrific in the sheep pasture. Any ideas how it might work out, or should I just save my time and plan to cut them all?

Sounds like an awesome field. I am sure you can cut these trees into any of the shapes you describe. Triangles, boxes, poodles, are simple. An archway that large would look great. Spiral is a little more difficult, but sinse your trees are so large you have lots of room for error. A wedding cake is not out of the question. There are many other simple shapes as well. I have done hearts, clubs, diamonds, and spades. How about a huge anchor? I had better stop now! hope this helps
Lois

Hi Lois,
Thanks for the encouragment.
It is a busy looking field, one that needs clearing to give the sheep some room to graze. Still, I hate to just cut down all those trees if I can have some fun with them instead. I'll post some pictures of my first attempts.