Here's what the AI managed to set up against my attack in October 1939 (I'm playing Germany, saved and loaded up as AI France):Our french AI needs to start its army buildup somewhat sooner.
https://drive.google.com/open?id=0B8SNzGSQSHgCQXROdUp1cDF5ZVU
Note: I did mod the game slightly, I changed factories to cost 10 instead of 5, and I messed around with the effects of Free Market and Central Planning.
France has over 150 divisions and probably could have placed a few more on the front line, but in general it seems the AI has a fairly logical defense set up. Britain doesn't seem to be helping at all, even though the war started 7 weeks ago. I completely smashed it though. They seemed to do some decent counterattacks and the Dutch were tougher to kick out of Rotterdam than I anticipated, but France basically failed to defend Paris adequately. I'm not sure if a human could have done much better.