They may look large and cumbersome, but the majority will still attempt to breed. My friend raises the large exhibition toulouse and his gander is massive, large keel, doesn't even look like he could hop on top the hens, but he got around 10 goslings this year so... Embdens are able to breed naturally, we have raised them for many years.
I think it depends more on the conditions that allow them to be able to breed especially for the toulouse. My friend had a large rubber water tub for them, and he has a pond that he will chase the birds down to, to breed when he has time, usually once a week or so. Though his geese don't like the pond and immediantly come back up, if I recall correctly the only one he has actually seen breed down there are his africans.