This.I would argue that the basic premise in that scenario is flawed, in that the French people didn't lack a will fight the Germans in the Second World War.
France fell because it was strategically outmaneuvered by the Germans, because air power and armor and had fundamentally changed warfare since the First World War, and because France did not have as anywhere near as much territory as the Soviets from which to weather early losses and continue fighting, or the English Channel to retreat behind.
Nevertheless the French military did fiercely defend the country. Keep in mind that the Germans lost about 27,000 men over the course of 46 days, which is close to half the number of of total KIA suffered by the US in the entirety of the Vietnam War.
France fought heavily in 1939-40, and then from 42 to 45.
In 1939-40 alone, french forces suffered 92 000 killed. Then 58 000 on the western front, and 20 000 killed in the resistance. French forces fought in Africa, Italy, and then again in France and finally invading Germany. Not that bad for a nation who had no will to fight.
The french plan for the war was not that bad, but was based upon two things that went wrong: first that USSR would not join germany (which was quite realistic), and then that Germany will not gamble the war launching a vast offensive in the Ardennes. Beside the Ardennes, there was the maginot line, and the first french army on the other side, which outrun the German in Belgium to fight them and stop them on a short front.
German gamble is 1939-40 is really a masterpiece; they won totally outmanoeuvring the allies, cutting the supply lines of the main french forces engaged in Belgium, passing through the lines. The true mistake in the french plan was that there were absolutely not sufficient forces in reserve, as such a rapid offensive in the Ardennes hadn't been even considered.
About a french/japan war during the WWII, where would have it occured ? France could not have fought a war with a big power in Asia, by any mean. Her army was designed to stop Germany, that's all. And I don't see how on earth could Japan have fought a war in Europe.
My guess is that Japan navy and air force were best by far, especially the navy, but the land forces were so different... difficult to judge, but Japan didn't perform very well against russia in 1938.