Yea, isn't is an accepted notion that Napoleon sold the territory (beside the need for immediate cash) because he knew he couldn't hold it against American intrusion (settlement); why not grab the bucks for something you know you are likely to lose control of anyway?
Napoleon launching an American invasion from Louisiana seems absurd even for this discussion. We would have to change an awful lot happenings in Napoleon's Europe to get an appreciable number of French troops into Louisiana. And then wouldn't the Brits recognize that Napoleon was over-extended and embargoed (harassed) the port city, or maybe even go as far to use the political circumstances to occupy New Orleans outright. I guess we would have to start with NO Trafalgar, because Napoleon would need one hell of a naval force to even begin thinking of an American invasion in 1806.
And we would have to include "No Haiti expedition" as well: whatever plans Nappy could have regarding Louisiana, they had been abandoned after French expedition force almost completely died on Haiti leaving Napoleon without a base for the future adventures in the area.