Evergreen might be difficult, but Cephalanthus occidentalis is a great native. A new cultivar is 'Sputnik'. Other natives that like wet include Clethra alnifolia and certain Cornus species. I think Viburnum acerifolium tolerates considerable wet also.

I've had alot of luck with Itea "Henrys Garnet" in a similar spot. Not evergreen, but the leaves cling to the branches for half the winter.
Also thriving in poorly draining wet clay is Vernal Witch Hazel, Pumilla Dogwood, common Viburnum Trilobum & "Red Wing", and Aronia Melanocarpa "Autumn Magic".
Cornus alba / dogwood gets severe leaf spot if too wet so had to move it.
My clay gets hard as concrete during dry periods so Clethra doesn't do well, and the Pumilla needs extra waterings.
Good Luck!