Go to the CO website, they should be able to tell you what you would be flying to Hawaii from Seattle. And that goes for any carrier. I found out in May of 2000, when I bought my tickets on AA to Hawaii, that in April of 2001 that AA would be flying a 767-300ER out of ORD to HNL. I also found out at that time that they would be starting a OGG (Maui) to DFW route in December of 2000.
As for the "little discussion" about the DC-10 vs. any other plane to Hawaii, there are very few DC-10's flying to Hawaii these days. I believe UA has one flight out of ORD on a DC-10 (which will change to a 767-300, then they are going to cancel that flight next year), AA has switched over all of their DC-10's to other aircraft (767's and 757's). HA flies the DC-10's on it's route's to Hawaii, but they are talking about getting ride of those planes. Delta never flew the DC-10 to Hawaii, just the L-1011, but they have or shortly will fly the 767-400 to HNL. NWA is the largest US carrier still flying the DC-10 to HNL. I don't think they plan on changing aircraft as of yet, like the rest of the carrier's. CO, I believe also, has gotten rid of their DC-10 flight in favor of the new 767-400.