Hi,
It is possible to get your dog and cat to get along with the bunny, but one wrong move and someone can get hurt, I don't advise it.
On another note, outdoor rabbits tend to have a shorter lifespan than indoor rabbits, in fact, most outdoor rabbits live on average for 3 years, where an indoor rabbit, depending on the breed, can live up to 12 years. Now if you live in a warmer climate than outdoor isn't so bad, but you also run the risk of having a less tame rabbit because of outdoor living.
If you let him run around the house he should get enough exercise, rabbits should be allowed to run loose (outside of their cages) for at least 4 hours a day. Always monitor him, bunny's are notorious chewers and not at all particular about what they chew, electrical cords (which can kill), furniture, you name it, they'll chew it. I have gotten a pet enclosure for my bunny's, that way they can hop around without constant supervision, get their excercise and stay safe.
Good luck with your bunny, and don't forget, a spayed/neutered bunny also lives longer, is less aggressive and easier to handle.

I've posted a picture of my bunny enclosure for you;
