OK, so AS may be Asian-heavy with partners, but alliance-free Philippine Airlines is starting MNL-SEA 3 weekly on May 3, 2020. I'm sure the Mileage Plan staff are on top of that one. PR MNL-SEA Really, I'm surprised DL hasn't grabbed this earlier since SEA is supposed to be a gateway to the Pacific.

Horrible Arrival time, though I suppose it could be good for connections
PR128 MNL2245 – 1945SEA 350 137
PR129 SEA2305 – 0335+1MNL 350 137