All dogs can be a threat to some degree and will aways have to be supervised when around your bunny, but I have to say that a breed that isn't intended for any purpose other than to be a companion animal would be the best. I'm suggesting you avoid breeds with stronger hunting/herding instincts, etc. Also, I think a less 'yippy' breed would be less stressful for buns to live with.
I have a pug and he is wonderful with the buns, but of course no matter the breed, all dogs can be different. The flat face (silly as it sounds) makes it tough for him to give a bite, too!
However, with flat-faced breeds (brachycephalics) you have to be prepared for certain health risks. They don't do well with very cold or hot temps and can seize and die when overheated. This is due to the inability to cool themselves properly because of the brachycephalic condition. They don't tolerate normal amounts of exercise well, and they often cannot swim. A life vest solves that problem though!
Of course, all breeds can have breed specific issues!
Do as much research as you can before you start meeting prospective pets. You don't want to fall in love with a dog that would be the wrong match! :wave: