According to Flightstats, your flight was cancelled at 17:21 DFW time, 1:19 before the scheduled departure time of 18:40 DFW time.
From what I can see, Alaska and American each have one flight to SEA after that time at 19:55 and 21:45, respectively. There are some connecting flights, but all that I saw (two) had travel times greater than 13 hours. Not many alternative for that route at that hour.