I think you're assuming that there would have been another option, which there wouldn't have been.

American commanders on the ground and in Washington would have know immediately that the attack was from the Japanese, as only the Japanese would have been capable of mounting such an effective raid.

There really couldn't have been another option. Even if the military was unaware of an impending attack, and even if the Japanese planes weren't identified as Japanese, it comes down to common sense.

No other country in that part of the world would be able to pull it off. Germany and Italy were too far away to make attacking Pearl Harbor even possible from a logistic standpoint. No ship or aircraft had that kind of range.