problem is that all of them put together dont have a snowballs chance in hell to deal with the soviets, logistics alone would keep them all from setting a foot on russian soil. there's also the very likely scenario of domestic worker uprisings and strikes in protest of the war and in support of the workers paradise(c)(tm).
Yes I'm sure that the average Josef Doev will fight to the death to protect the Soviet Union from the imperialist polish and rumanian troops (excuse me invade Poland). As he fought the Germans in 1941 when most of Soviet Union soldiers or citizens don't know about the genocidal german army and welcome the germans troops with bread and salt.
In 1921, famine had killed 5 millions people in the Soviet Union...
And the Soviet government just went over the Orthodox Church. In this year also, the Soviet Union had difficulties to put down the Kronstadt revolt and the Tambov area uprising...
Then you have the NEP period and in 1928, the Soviet Union just restored its economy to the 1913 level. With around 10M citizens less...
The second problem is that the threat of a communist uprising in France was rather inexistant.
And the best exemple is how quickly the french autorities disband the French Communist Party in 1939, even the communists newspapers were forbidden. Or how many french communists left the party and reaffirmed their commitment to national defense. When the Molottov-Ribbentrop Pact was signed in August 1939, many of the french communists rejected the pact, and left the party, only when the Komintern ordered the French Communists leaders to be against the war, a part of them fled the country, the others were arrested.
And who did it, some right-wing fascistoid government ??? No Edouard Daladier from the Radical Party (centre-left).
Was the communists supported by others leftist ? Leon Blum from the SFIO (socialist) claimed that the PCF should not be forbidden (because most of its leaders and members were against the pact) but the french communists who were traitors should be executed by firing squads.
At the height of its popularity, in 1936, the PCF represent around 15% of the votes but the left was rather loosing support after 1936.
And in this case, the french army will be rather fighting directly the "Boche" and not the workers paradise soldiers. And once a war begin, it is rather unpopular to begin striking and be a de-facto support of the ennemy. In July 1914, Jean Jaures who was against the war, was shot and severals days after his murder, french socialists were in the "Union Sacrée" government.