While I have heard there are nonstop flights between one of the 3 Washington DC airports and Vancouver (YVR) I have never in practice been able to find one. Are there any regular nonstop flights between Washington DC and Vancouver Canada?
There is a seasonal flight between IAD (Washington Dulles) and YVR (Vancouver International) by United Airlines/Air Canada. Here's an example search on Kayak.
Rome2Rio says that united offers direct connections.