1. Why would the US be at war with Germany in 1942? Just saying it doesn't make it true, hell if Hitler didn't declare war himself on the US after Pearl they wouldn't have been at war in the first place and for the US Congress to pass a declaration of war against Germany without an initial declaration is dubious.
I'm sorry for all, but I'm pretty sure that the USA declaration of war against Germany was only a matter of time in December 1941. And the sinking of too much US merchant ship or the attack and the sinking of an US Navy ship will be the reason for FDR to declare war against Germany. This will probably happend in 1942, spring or summer...
And the changes of this TL don't affect the decision of FDR to make war against Germany.
There will be no Pacific War because the Japanese are fighting a war against China and the SU and they will not attacked new ennemies : western allies or the USA. But the war in Europe and Africa will happend as in OTL.
2. The US didn't declare war on Germany for its submarine attacks on its shipping in the Atlantic, why would it declare war on Japan for doing the same in the Pacific, not only that but its absurd to think the Vladivostok route would actually be usable in the face of a IJN blockade, in the Pacific the convoys won't have just submarines to worry about like in the Atlantic, the entire Japanese fleet will be hunting them down. Trying to run a blockade in the middle of 2 foreign power's war and then crying because your ships get sunked is stupid.
I'm sorry your POD is completely seperated from OTL facts.
In OTL :
In 1941, the US Navy ships escorted Allied convoys and opened fire upon German ships or submarines if they attacked Allied shipping within the U.S. Navy escort zone.
Roosevelt was firmly committed to the Allied cause and the "Atlantic Charter", the "Victory Program" and meeting with Churchill had been made before the US entry in war.
Again avoid the Sterotyphe/Cliche about Japan, the Pacific war will never occur in this scenario
Which Sterotyphe/Cliche about Japan ?
That except killing korean, mandchurian or chinese civilians and fighting unexperienced and undersupplied chinese armies, the Japanese army or navy had zero chances to win against any major power of WWII, the UK, the USA or the SU...
The Japanese were victorious during 6 months, after they were only loosing except some tacticals successes. Yamamoto was sure of it before the war...