Were your bags tagged through on the original DL flight from SEA?
If so then this is clear cut EU261 case. They couldn't have done that otherwise. The question then is why did system show you needed to be rebooked. Was it weather and then they found crew? ATC reduction and then allowed? Etc... Since both DL and AF/KL system showed cancel, something happened. Beed to know what to determine if compensation applies.