I dont know what the minimum connection time at ICN is. If you're booking on one ticket then it shouldn't let you take connection less than the MCT and so protected in the event of misconnect. If its separate tickets then you're on your own if misconnect. IIRC ICN-SEA only has one flight so a misconnect means waiting another day or two, unless you can get rerouted ICN-YVR which doesnt operate all the same days and I wouldn't hold out hope of such a last minute change.

Most of the time, getting to destination on a certain day or time is more important than the difference in seats or ife, and so I would take an earlier flight.