I don't have figure for french soldiers, but something can be deducted from French officer's background :

According to "Nouvelle histoire de l'armée française" by Serman/Bertaud, Fayard, 1995 :

a) In Ancien Regime army
Colonelcy was forbidden to non-noble
"Petite bourgeoisie" could not go further than NCO
30% of rank-and-file came from cities, which totalled 15% of the population.

From other sources : rank-and-files were so low in social scale that theatre and public gardens were forbidden to them.

b) In Imperial Army

77% of the officers of the napoleonic era came from rank and file.

Proportion of officers coming from school decreased, from 17% in 1805 to 7% in 1815.
Amongst all officers, 17% came from Ancien Regime army, 23% from 1792-1794 Levées and Volunteers, 60% were promoted afterward.

The social origin (father profession) was :
(I didn't translate to avoid inadequate terms)

(Infantry Cavalry)
Bourgeois 34% 34%
Militaires 9% 14%
Hommes de loi 5% 4%
Artisans et agriculteurs 25% 18%
Ouvriers et journaliers 0,3%
Non précisé 27% 30%

Some guests from this figure :

The Ancien Regime army had :
- an ageing, literate petite-bourgeoisie stopped at NCO ranks (as can be noted in the biography of several french imperial officers).
- a large proportion of urban soldiers probably coming from the lower classes of unemployed workers and servants, a manpower more illiterate and despised than the small peasant land-owners.

The liberating effect of revolution can be seen in the large number of literate men who were drafted by the Revolution and Empire as rank and files and could go further as NCO and then officers; and the opening of the officer ranks to all social origins, especially "Artisans et Agriculteurs".

It would be interesting to compare this figures with social origin of officers in UK, Austria, Prussia, Russia ?

Regards,

Jean