I have a very, very expert garden mentor, at it for 45 years, who espaliers everything he damn well feels like, flat against the walls. Witch hazel (a Corylopsis relative) is one of his real masterpieces. It blooms in late winter, then has pretty leaves like the winter hazel I like so much. Its like a giant flat fanned pinned to the fence…amazing. You have to be fearless enough to cut out branches and create an architecture that is both pleasing to the eye and to the plant, and keep at it so the plant doesn’t misbehave and outgrow the concept of espalier. I have a fantastic espaliered Asian pear (photo attached) on the south side of my house, and I have to trim it twice yearly or more to keep it from becoming a monster, but it’s beautiful all year long. (This year it bloomed very lightly as you can see, after a super-heavy flower and fruit crop last year). The thing about Corylopsis is that its flowers are unpredictable after a cold winter in Zone 5, so you’d want to grow it for its structure and foliage (which both are nice). Remember that with deciduous things like this or the rose Blue Arrow suggests, that much of the year they will be leafless–so structure "naked" is important. The pear really has it bigtime…the rose not…the winter hazel in-between. How much light is there on your east side? That’s the other deal with what you choose…east sides can be low-light. So what I’m saying is: what season of interest do you want to get from this plant (one or multiple) and what light conditions are there? You can espalier a lot of different things (like my mentor)…but nothing will like it if the conditions aren’t correct, and you won’t like it if it’s a spot you view 365 days and it’s not a 365-day plant.