You could always try one of the red twig or yellow twig dogwoods. They would get a nice size in a large container and would have 4-season interest. There are some that have variegated leaves too and others that have color gradations that go up the stems from a red at the bottom to a yellow towards the top. You could also try an itea and get some nice fall leaf coloration, a pee gee hydrangea with late summer blooms or even a lilac (eg., the preston hybrids which are later blooming and very hardy). Most of these that I listed are hardy in Zones 3 - 4. I am growing the shrubs I listed.

For a hardy tree in your zone, you could try an aborvitae (Thuja occidentalis) or an alberta spruce. I'm growing a plum tree myself. It's going into its 2nd leaf and just bloomed for the first time starting yesterday!

In general, you want to aim for plants that are hardy 1 - 2 zones colder than you, so look for plants hardy to Zones 2 - 4. With a little protection, you could try some Zone 5 shrubs/trees.