Britain and America? Stalemate? Dreaming...
A super-Fortress Europa could begat full deployments of B-29s to Europe. And later, nukes.
The really scary idea about nukes against the Nazis is that I could easily see Hitler holding out somewhere saying "Bring it on!", while Germany is reduced to ashes around him. Some might say that that was already happening, but those are the same "some" who claim that the Bomb was an unimpressive tactical weapon doing little damage to the enemy. FDR just wanted to spend $2,000,000,000 in 1942-1944 dollars to construct a weapon that might not even work solely to scare the Uncle Joe that he was certain he could work with. As to that logic, see my sig below.

The USSR could be forced into a Brest Litovsk treaty. Anything more is impossible and the Nazis would never go for it. The US is to far away for Germany to seriously effect it. Britain is beatable though. US > USSR > UK.
The OP says all the Western Allies. That means Britain, her Empire, the Dominions, and the USA. Germany could make more U-Boats sooner, at the cost of tanks for the army, leaving the East vulnerable. Fighting against only the West the Germans can't scrimp on the Luftwaffe. A bigger U-Boat menace means even more ASW assets and faster introduced ASW technology.
No way the Nazi could have win against Allies or Soviets
too low number on troops, lack of resources and Morons in leadership.
lets take the USA
as Hitler declare war on USA, they switch from Car industry to Aircraft and Tank production for over 3 years.
while german industry had low production number and scarcity on material and Luftwaffe changes there mind on top priority Programs.
Produced the American Bombers and Fighter aircrafts on mass, like the B-17 Flying Fortress they produce 12731 units (1) and bomb The Third Reich back into the stone age. (2)
the Wehrmacht learn the hard way that American troops are armed to the teeth and were experienced shooters (3)
The Soviet make a total mobilization, in the end 6.4 million Red Army troops were pushing at East frontline, the 1.5 million survivor of the Wehrmacht back into The Third Reich
They produced massive low tech like the T-34 tank, were they make 64549 units and throw them against the Wehrmacht and SS Tanks divisions with success
Hitler reaction on that was he ordered construction of bigger tanks, with bigger guns, which led to Panther, Tiger and Königtiger tanks and infamous MAUS prototype, each one heavier, more complex, and more petrol thirsty than his predecessor. Build in lower numbers as Soviet counterparts due to lack of resources. (4)
1) Not to mention 15000+ B-24 Liberators,

many going to Lend Lease ASW. They closed the gap between Europe and America for the U-Boat scourge. Poor B-24s. Longer ranged and much bigger load than B-17s, yet they never get the notice the Forts do.

Despite all their good works against the Japanese captured oilfields in the DEI, plus Ploesti.
2) Well, the 19th century, anyway. Or Germany about halfway into the Thirty Years War.
3) But Americans had their own problems, including a lack of tactical sense that caused them to attempt bizarre and often unwise moves against the enemy. So too their most junior officers in the army tended to be poor until they got serious combat experience (if they lived that long).
OTOH, the Americans had considerably greater technical expertise than their Allied and Axis counterparts and were incredibly fond of captured equipment. They were able in tight combat circumstances to employ captured enemy weapons of a sophistication that most armies wouldn't attempt to try to use (frex, satchel charges, flame-throwers, AT/panzerfaust/panzershreck missiles).
4) Not to mention using slave laborers (5) rather than employing loyal German women as "Reni the Riveters"

Or God Forbid, Jews, who could be forced, by direct threat to their families, to give superlative output to save their lives. As the Jewish refugees escaped from Eastern Poland did when they reached Japanese-occupied Manchuria. They did outstanding work for Japan in their Manchurian factories, in exchange for their loyalty given to Japan and Japanese good sufferance of their presence.
5) The Germans may have increased the QUANTITY of their industrial war output, but their Quality Control had turned to shit. Many an artillery shell would land among Allied troops in 1944-45, turn out to be a dud, and when the UXB people took it apart, would find it loaded with earth or salt. With a little message inside, written in Russian, Polish, or Czech, that said: "Good Luck! Happy Hunting!"
