The 2 bags we have are 17x24, but have wheels, which makes them closer to 26, so I know they wouldn't be allowed as airline carryon due to the size of the overhead bins. However, laying flat on a scanner, there would be no problem going through. We've carried on in Galveston, Miami & Ft. Lauderdale and all those scanners were larger than airport carryon scanners. Never been to the Seattle port so no clue.
And as for those who worry about me handling my luggage, believe me, a 39 pound suitcase is not an issue for me. I have taken my own luggage on board on many cruises - ever since hubby's cuff links went missing. Why he put them in checked luggage is beyond me.
As for those who say the risk is too small to worry about, it's all gonna be okay - until it isn't. A 1% chance of losing your luggage is no big deal until you are in that 1%. And yes, I worry on the flight as well, but just don't know how to pack for Alaska in an airline carryon.