So I would like you to tell me which subspecies of cackling you think it is?
Also concerning your Hybrid: Please see here a substantial number of photos of GWFG x Cackling goose, thanks to Dave Appleton, Cathy Sheeter, Steve Mlodinow:
Greater White-fronted Goose x Cackling Goose (possibly Taverner's Cackling Goose, race taverneri ) hybrid, Aurora (Colorado, USA), 8th De...
birdhybrids.blogspot.com
and a few probable GWFG x Canada
Greater White-fronted Goose x Canada Goose hybrid, location not given (probably Colorado, USA), 25th December 2013 - copyright Cathy Shee...
birdhybrids.blogspot.com
I don´t think it is so clearcut and easy (I have been interested in ID of hybrid birds for 30 years now), but there will always be things I do not know yet
...and therefore I would like to learn about that Facebook guys reasoning why Cackling x GWFG?