whooping crane

Cranes or Herons?
I can not tell if this pair are white morphs of the Great Blue Heron or Whooping Cranes. This is in an area where there are both herons and a huge number of Sandhill Cranes. (At one point they were working on having whooping cranes assisted by sandhill cranes.) This spotting was in October - migrating southward. I only saw this pair once at a pretty far distance. Even with a long lens this was the best I could do. Perhaps someone who is more familiar with posture and body/neck shape would be able to tell which bird this is.