This question breaks down into 3 parts. (1) what is legal, (2) what normally would happen and (3) what could happen.
(1) It is legal for one parent to provide the informed consent. It can be either parent.
(2) Normally the OB/GYN or Pediatrician would be aware of the mother's feelings about the issue and if there was a dispute between the parents, would demure until the issue is resolved. A father would be suspect if he suddenly showed up on their doorstep with a baby wanting a circumcision and the physician would probably investigate further before performing the procedure. That would be for the physician's own legal and ethical protection.
(3) If the physician strongly supports circumcision and is unethical, it is possible he/she would perform it. If the mother had made her intentions known to the physician, he/she could be in for some legal problems.
I have no doubt it has happened and will happen again. I know one man who went in for a vasectomy at age 42. His wife conspired with the surgeon to have him circumcised and it was done. That was neither legal or ethical but it happened.
The best thing is to have a birth plan that clearly spells out "no circumcision" and make sure that all of the care givers are aware of your feelings beforehand. That includes the OB/GYN and the pediatrician as well as nurses. If this is done, it is highly unlikely that a father would be able to get it done. If the father knows there will be hell-to-pay and that all concerned have been put on notice, it is even more unlikely to happen. If there were a court ordered injunction with the potential of jail time, that would be even more of a deterrent. I know of a divorced New Jersey couple who took it to court because the mother wanted the circumcision and the father didn't. The father was afraid it would be done against his wishes and filed in court, getting an injunction until the case was settled. In the end, the court sided with the father and the baby won.