Everything I've read has stated a different means of entry of the US into war against Germany.

The Axis, Germany, Japan and Italy mainly, had a mutual defense pact. They would all go to the aid of any party which was attacked.

After the bombing of Pearl Harbor, the US declared war on Japan. Some members of Hitler's inner circle pointed out that the pact called for assistance only if the member were "attacked", and the US had not attacked Japan.

Hitler pondered this a while, and then decided the spirit of the agreement called upon Germany to enter the war on Japan's side. (Tolland)

Not that Hitler would have cared about the pact - he made a joke once about looking for all the treaties he'd signed and kept. He said he was still looking.

It was only after Germany declared war upon the US that the US reciprocated. I've never read anything about American plans leaking that did it.

(By the way, the reason the B-29 was available so rapidly was pre-war planning for a bomber which could reach Europe and return to North America without refueling after England was invaded. So there was a lot of planning.)

Arf