My son has a boxer, Sadie who I believe would be great with my girls. They try to peck her nose & tail every time she is around the pen. When the girls were a couple of days old, I tried to introduce her to one. She so gently opened her mouth, expecting me to give her a new squeak toy. NOT.
On the other hand, our shepard/husky mix is very aggressive & the girls run in their coop when he is around. He is why I will not free range. I am so scared that someone will let him out of the house. I won't even open their pen/coop if he is outside.