Yes, trees work fine in urns and other containers. Be sure to choose urns that have drainage holes, so excess water can escape. If the urns you choose have a central drainage hole in the bottom, I recommend covering it with a piece of non-metal window screening. That will keep the dirt from sifting through and blocking it.
Do not use garden soil in the urns. Buy a good potting mix designed especially for container-grown plants. Look for words such as "potting mix" or "for potted plants" on the label. Of course, you can mix your own, but you would have to be somewhat experienced at growing plants in containers in order to understand what components to include in your mix and how to make sure it will drain rapidly enough. You may well have that experience, but since you didn't mention it, I thought I'd better touch on the subject.
I think I would select a dwarf variety of the evergreen you decide to plant. Being grown in a container will cause some additional dwarfing, which will help keep the plants to a manageable size.
Since you're located in CT, you might have to provide some protection for the plants during the winter. The roots of container-grown plants are more subject to damage from freezing weather, since they aren't surrounded by a large volume of soil the way the roots of in-ground plants are. I recommend that you check with a local independent nursery, perhaps the place where you buy your trees, for advice on whether winter protection will be needed.
Welcome to the forum!
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