This is more a plant choice question than a landscape design question so you will probably get a more targeted response over on the specialist Hydrangea Forum.

I would recommend one of the hydrangea paniculatas for that amount of sun, as paniculatas are more sun tolerant than the others and are very winter hardy to zone 3. They will tolerate clay soil in my neck of the woods. Just make sure that you can provide soil that is as evenly moist as possible (no periods of dry, wet, dry, wet, etc). Feel free to provide organic compost in Spring and amend the soil in Spring & other times if it is very alkaline (amend it again if the leaves turn light green or yellow, except for the leaf veins which remain dark green). Choose the specific paniculata that you want based on your bloom likes and based on its estimated size at maturity. For example, Little Lime, Little Quickfire, Strawberry Sundae, Baby Lace and Bobo are all compact. The others tend to get around 8' or more. Except for Little Lime and Limelight, the others have blooms that start white, turns shades of pink and end up brown. LL and Limelight start lime, turn a shade of white (more rapidly in very bright conditions), a shade of pink and then brown.

I did post this to the Hydrangea Forum as well, thanks floral_UK. Figured I'd cover all my bases! Luis, thank you for the feedback. Through research, I see there's a paniculatas called Polar Ball, I really love the round shape much more than the cone shaped ones. I appreciate your advice!