What do you mean by "sound like"? The most unusual-for-a-Romance language phonological features of French - dropping the final vowels in the feminine, and the uvular R - are both quite recent, going only about as far back as the 18c.
The uvular R was a Parisianism that became fashionable after the Revolution; most historical linguists seem to think that all uses of uvular R in Europe derive from that, in the 18-19c. This is not hard to butterfly away.
The final vowel loss in the feminine is a bit harder to avoid. (In the masculine, vowel loss happened centuries earlier, but it also happened in Occitan and Catalan.) The Gallo-Romance languages all reduced historic final /a/: Occitan pronounces it /ɔ/ (Toulouse is pronounced /tuˈluzɔ/), Catalan /ɐ/, and the Gallo-Italian languages range from /a/ to null. In French, it was /ə/ for centuries, and was the only exception to otherwise regular final-syllable stress.
You could argue that the development of uvular R made the vowel loss easier, since the uvular [ʁ] is less sonorous than the tapped [ɾ], which means it's possible to pronounce words like "mètre" with one syllable if it's [mɛtʁ] (or [mɛtχ]), whereas *[mɛtɾ] wants to have a schwa on either side of the R. But, well, the final vowel loss happened after every consonant and not just /r/.
Still, the fact that the final vowel is stable at /ɔ/ in Occitan, to the extent the use of Occitan is stable, means it could have stayed. You might not even need a special POD for this - language evolution doesn't always happen for a reason. Not everything can be randomly butterflied away - again, the final vowels did get reduced in all Gallo-Italian languages - but some things can.
If you want a political POD, have the French Revolution not happen, and instead give France riots beginning in the South, escalating to civil war in which the Gascon and Languedocian liberals triumph over the Parisian royalists. The prestige dialect would move south. If the resulting political regime were centralized (in the same way that in 2011, Libyan rebels were adamant that Tripoli is the sole capital even when they held Benghazi and Qaddafi held Tripoli), Parisian French would still dominate, but it would take in some Southern flavors.