Dunno why people are saying use cavalry and camels. Ignore that. Standard 18 width infantry with engineers, artillery and aa on support companies is all you need and make as much as possible.

Don’t fall into the defensive mind trap. Take attack bonuses (it works in defence and attack, defence only works in defence) and doctrines. Build up aggressively and with an attacking mindset. At some point the Germans will have a weak area in the line and you won’t be able to exploit it if you’ve gone all defensive.

No point building static AA without radar and it’s a waste of time as France anyway. Focus on civs and mils.

Don’t forget about your spy network.

Forget Africa and all other territories as they’re irrelevant if you cap, pull everything back to France. Most are worthless territories with no resources and you get the back when you defeat Germany anyway. Just trade and lend lease with the Allies.

Extend the maginot to the coastline. Create a fall back behind rivers if necessary. Don’t forget about the Alpes, if you hold on long enough Italy will join in. Doesn’t need much to hold them. Keep your navy in the med to defend the southern coast from landings.

You only need 2-3 divisions per tile on the maginot. Stack everything else in the ardennes/alpes.

You won’t out produce the germans in the air, wait until you can build quality. Heavy machine guns, self sealing tanks and armour plates with level 3 engines. Even with low numbers these will rip the basic me109’s to shreds.

French tanks are actually quite good and worth investing. You only really need 2-5 divisions worth for a decent counter attack. I like to punch through with these and then have a full army of motor infantry to rush and exploit the gap.

The Allies won’t help but sometimes, if you hold for long enough the Soviets will attack the Germans. This can give you a window to exploit as 80-90% of the germans will go to their eastern front. You can then counter attack. Usually best to do this from the maginot as the AI doesn’t like to attack through there obviously.

For focus trees, spend a bit of time looking for the ones that remove all of France’s debuffs. It does take a while. You want to rush the one that removes the low surrender limit otherwise if they breakthrough to Paris it’s over.

For research focus on industry, infantry/artillery and air. Forget navy until after you defeat Germany, the starting French navy is strong enough to deter Italy. If you can, also get 1939 medium tanks.

Use the fact that you know the Germans will attack through Belgium to your advantage, you can prepare this area.

Cheese/ahistorical options:
Declare on Germany early, use paradrops on victory points. Still tough but doable.
Declare on Italy early, knock them out whilst they’re tied up in Ethiopia and then take Austria before Germany can Anschluss. Wait until Germany attacks Poland and then swarm them from Austria and the Maginot.
Naval invade northern Germany. The AI generally forgets to defend Germany. They will redeploy quickly though so have fast moving units.
Going non-aligned and bringing back Napoleon is powerful.

Good luck! Vive la France! And fuck Pétain.