Not really.
Ireland flipped from mainly Gaelic to mainly English pretty quickly in the 18th/19th centuries. Only through a big effort by the educated elites did it not totally die out.
Just have one language be seen as the language of rural hicks which offers no opportunity in the world and the other being the language of culture, business, learning, everything, and speakers of the lesser langauge will even begin to grow ashamed of themselves and actively work to ensure their kids don't have the same disadvantages.
Your forgetting national and emancipation movements. IOTL in Belgium the elite, even those from a Flemish background (who did know Dutch BTW), spoke French. Starting from the Great War, from which there are annecdotes of communication problems between Flemish soldiers and their Francophone officers; the language struggle really fired up in the sixties. Furthermore the Walloon industry went into decline and the Flemish region became the most important economic region.
Naturally with this background Franchifying the Low Countries is especially a sensitive topic in the Flemish region, since (upto a certain degree) this was how they felt the Francophone Belgian elite behaved.
And in previous centuries from the Burgundian Netherlands and the Northern and Southern Netherlands, there were some conflicts with a most powerful (and thus dangerous) neighbor France, especially with ambitious French rulers dreaming from natural borders...
The Revolutionary France and Napoleonic France made the greatest acquisations, Revolutionary France annexed the Southern (Austrian) Netherlands in 1794 and in 1810 Napoleon ended the kingdom of Hollland (Northern Netherlands) and made that a part of his empire too.
Having Napoleon succeed could be pod.
However 'la Grande Nation' has more means and the Low Countries in your scenario could end up as the Alsace and French Flanders. OTOH by the 19th Dutch was a fully developed language, so they have a better starting position than the Alsace and French Flanders; which wouldn't prevent French turning into the prestige language, but it does help the Dutch in managing to keep enough national identity to have minority rights.
Furthermore this France probably will face problems with national and emancipation Dutch movements or even Dutch revival movements (and I'm sure France's neighbors don't mind that France is being distracted). For instance IOTL the Czechs also rediscovered their Czech roots...