Kevin I suggest you refrain from answering questions when you don't know the answer. There are several different species of geese, Only one species of dogs, The two domestic species can cross with each other. Canada are a different species, fetrile maatings are rare but sometimes happen, much more like Mules than dogs!
How can you tell if a canadian gosling is mixed? There is an auction listed in the selling area that has a canadian mixed gander with 2 canadian geese, but there are other geese in the same pen I assume. So if the canadian mixed gander should be sterile, this means that any eggs laid by the geese would be mixed, thus being sterile as well? But how would you tell if the goslings are canadian mixes?
The greylag and the Asian geese from which most domestic geese are descended are from the same genus - The Greylag is Anser anser and the Asian Swan goose is Anser cygnoides. The Canada goose belongs to the genus Branta. That explains why most crosses with domestic and Canada geese are likely to be infertile. Most domestic geese whether from the European Greylag (Pilgrim, Sebastopol, Toulouse etc) or Asian Swan goose (Chinese goose etc) belong to the same genus and are closely related with the offspring most likely to be fertile. Even with distantly related crosses the odd fertile hybrid has been known and in domestic breeds of birds such as canaries breeders have used fertile hybrids to introduce new traits and then breed out the introduced genes over generations to establish a new pure breed. But in every case it took huge amounts of trial and error (mostly error and failure) and many years, even lifetimes of painstaking work to get there.