How about 2 adults and one 75 pound Bernese...
How about 2 adults and one 75 pound Bernese Mountain Dog? Would a 3-person be the way to go or would it be fine in this 2-person tent?
So, basically, three people. If the dog is coming with you, get a 3P tent. You'll be grateful for the space.
I don't think you would be very comfortable with 3 "people" in this tent. It is roomy and you can make do in a pinch, but if your dog is going to sleep in the tent with you, I would go with the 3P. If the dog is willing to sleep outside in one of the two vestibules, it could work (although the vestibules are on the smaller side.