[seszett]

The version of French that became standard French was not exactly the language spoken in Paris (the local Parisian accent has mostly disappeared now but it can be heard in old movies) but the one spoken in Western France, where the French nobility lived and spent time (the Loire valley is now known for the castles they built there).

In addition, when the colonists settled in New France and mixed together, standard French (the concept probably wasn't there at the time, but administrative French maybe) was the natural common denominator for them.