Whether you choose a rose or a clematis you are going to have to some serious soil improvement as both are hungry, thirsty plants and will need all the help they can get to establish and grow. Dig in plenty of well rotted garden compost and manure to as wide an area as you can.
Roses that will grow on a north facing aspect are Golden Showers - scented yellow flowers; Teasing Georgia - also yellow, scented and repeating; Iceberg - white, repeating; New Dawn - pale pink and lightly scented;
For clematis, there are loads of possibilities. I find the group 3s easiest to manage as they are pruned back hard in February or March depending on your local climate and then flower all summer on new growth. Betty Corning is scented; Duchess of Albany has strong pink bell shaped flowers; Gipsy Queen is a deep, rich purple with a redder stripe but you may want a paler colour to stand out in shade; Caroline has pale pink flowers for months; White Magic has pretty white flowers. If you prefer a group 2 that will flower in May and June and then again later in summer, try Silver Moon. You can check all of these here - http://www.clematis.hull.ac.uk/new-clemlistsearch.cfm and then maybe order them from a good supplier such as http://www.taylorsclematis.co.uk/ or http://www.thorncroftclematis.co.uk/ or http://www.simplyclematis.co.uk/
Remember to plant roses so that their graft union is a couple of incjes below the soil and clematis at least 4 inches/10cms deeper than they were in their pots and then feed and water them well till estabished.