I would NOT recommend the 2 breeds together. Not that they won't get along.......they probably will. BUT, they are very different energy levels and play abilities. I babysit my friend's english bulldog from time to time and it has made me realize that boxers and bulldogs are not a good match at all. The bulldog wants to play like the boxers do but because of their extremely smashed faces, they don't breathe well. They can overheat quite easily and the vet has told my friend not to let him get too overworked or he could overheat and die. So the entire time I have my friend's bulldog, I have to give constant time-outs so that he doesn't get too overheated. Usually he can't play/wrestle for more than 10-15 minutes at a time before he can barely breathe and I have to separate them. Just my opinion but I would never own the two breeds together.....
english bulldog is nothing like the american bulldog. in fact, there are two prominent types of american bulldogs, the Johnson and the Scott (Standard), and both differ dramatically from the english or french bulldog. The johnson is short, wide, very short muzzle, very muscular, high back end, and low-wide front end and can weight up to 125lbs. The johnson american bulldog is not a very good work dog in most instances, wears out quickly because of bad breathing, and though they look "tough" he is structurally inferior with many health issues stemming from the breed being formed into what it is today. The scott or standard is a hard bodied, solid, very muscular, working breed dog that is taller, narrower, VERY athletic, and plays very hard. He is generally lighter than the Johnson but is far more agile. He has a longer muzzle than the Johnson bulldog which allows him to breathe easily and he is very muscular. They are primarily used in OB, Schutzhund <sp?> training, protection work and as hog catching dogs. They are bred first and foremost for temperment and so their temperment with humans and kids is almost spot on with the boxer. You will never meet an american bulldog who is aggressive towards humans unless explicitly trained to be so. They are particularly known for their fondness of children and family and will stop any threat in its tracks before harm comes to somebody in
its family, but being bred as a catchdog and family protection dog for so long, they sometime have problems with other dogs who try to dominate them.
a good site to look over for temperments of the american bulldog is
http://true-grit.org/smf/index.php?action=forum
there you can see pictures of both the johnson, standard/scott/performance, and some hybrids. The american bulldog is a very loving dog, and true companion, but doesnt always do well with other dogs if the other dog is a dominant dog. The AB likes to be the dominant dog and will usually make sure its known.