American Bull Dog and ???

[Bahamutt99]

My main issue with picking certain breeds is how common are they? I've never seen a Landseer, but they could be more populous elsewhere. Therefore, what are the chances of having a mix of one? Same with American Bulldogs; I've only seen them at weight pulls. I can't really tell too much from the pictures given, just that he doesn't look like he's got bull breed in him.