I am looking for a very small (say 8'x8' at maturity) very fragrant tree with blue or purple flowers. It will be planted at a South-West-facing location with 2 to 3 hours of afternoon sun and dappled shade for the rest of the day. I am in Ontario, Canadian plant hardiness zone 5a bordering on zone 5b, about equivalent to USDA zone 4b.

Any suggestions? Thanks!