Forgetting that BC exists entirely. If you search "Kei" on Craigslist Vancouver, there's currently 37 postings, and they're constantly being imported here. I see them in Washington as well, although those may be Canadians just visiting.
A notable difference being in Canada you can import vehicles at 15 years old rather than 25. There is a decent flipping trade in Vancouver to import JDM vehicles while they are Canadian eligible but not US, hang on to them for a while, then sell them south once the 25 years are up.
At least in some parts of Seattle, you do see them a lot. In my neighborhood of Ballard, for instance, I can go for a walk and see three of them parked on the street.
It probably varies quite a bit by which part of the PNW we're talking about. They're exceedingly rare in Oregon (and I'd bet they're visitors from Washington or BC), I haven't seen one in many years.
They seem to be popular in rural areas of Western Washington. I saw several while visiting the San Juan Islands last year, and have spotted them fairly frequently on the Olympic Peninsula - along with other fellow RHD Japanese imports like the Mitsubishi Delica and Nissan Skyline.