A. I would recommend a clematis called 'Prairie Traveller's Joy.' It is very hardy, unusually vigourous, and produces small white flowers in mid- to late-summer (unlike many clematis cultivars) that do not seem to attract pollinators. It still sports the interesting seedheads.
Several years ago, I planted one on each side of both our arbour and a seating nook. By the end of June, I found myself cutting the vines back just so that we could walk through the arbour. The nook is a wonderful shady respite when my gardening chores have exhausted me.
Master Gardeners of Ontario