Canada

I think the only way you'd figure it out would be field ambush hunting where you can get a good look at a flock as they come down in a pea field or something. It doesn't sound like they migrate together and their flyways might be fairly predictable for targeting hunting areas.

But other than size which is hard to judge on the wing, I wouldn't take a shot based on that.

I know a lot of people are instinctively against hunting, but with massive food availability on harvested fields in wintering areas with no predators, these species can grow out of control very quickly. Snow geese are devastating arctic areas that are very slow to rebound because of the sheer numbers and lack of hunters. I had heard about this sort of concern with mixing up swans with snow geese, though that's a lot easier to identify on the wing so I don't think there's been much bykill from that.