Geese are not guard dogs. Watch dogs maybe, they will alert you by honking when something is up, but really they are only protecting their own kind.
Rarely will a goose fight back for an animal that is not a goose in its family, and even if it did, a goose cannot stand up to a fox or a coyote. Maybe it could scare off a raccoon, but geese are birds, they're not equipped to fight with any living thing other than its own kind. Please do not get geese and expect them to be able to fend for themselves.
If you want an animal to protect your ducks, get a flock dog. The Great Pyrenees is very protective of its flock when raised with them, they will bark to alert, and if the danger persists they will normally fight back. Not many animals will come into a yard with a 100lb barking beast, but even then you need to have a secure house for your ducks to sleep in at night.
If you still want geese just for pets, the American Buff goose would work well. They're extremely calm, very friendly, very quiet. They're like the Toulouse but not as aggressive/territorial. My buffs are the calmest out of all my breeds, and they pick the least amount of fights. So my personal opinion would be that Buffs could get along with your ducks.
I don't think you'll find any goslings this late in the season, consider adopting some adults? Maybe some that were already raised with ducks.