Without meaning to sound rude but is it an American thing, wanting to landscape your rental property? I can certainly understand a pot of flowers or something beside your front door but this (much like an earlier query) goes beyond that...

Vikingboy, could you post a picture of the area so that the responses can be better focused?

Canadians don't plant up their garden areas when the rent? Back in the day when I rented, I don't think I lived anywhere that I didn't do at least some in the ground gardening, but I'll admit that while living overseas, most of my rental gardening was limited to containers on terraces/balconies. Back to the question at hand, a picture would help a lot. When you say walls adjoin both sides, do you mean house walls, or lower landscape walls? It sounds like you would be best with plantings that take both sun or shade. Narrower growing plants that might work could include Foxtail Asparagus ferns, Dwarf Heavenly Bamboo, Neomarica caerulea, Cyperus textilis, Dianellas tasmanica, Impatiens soddenii, Leymus condensatus 'Canyon Prince', Fatsia japonica, Francoa sonchifolia, to name a few things that would fit into narrow areas and take shade or part sun. Most of the above are more foliage than flowering, but there are also some above with good color in season.