First, as Dave said, the economy will be buggered before the French can intervene. It isn't a matter of America being self-sufficient in food or gunpowder or anything else. I doubt anyone's arguing that America can be starved into submission. It's a matter of the flow of money - and a blockade stops that.
American Revolution, there was no money. everyone did it for free because they believed in the cause. many didn't care that there was no money. however, in the cases of those that did, they were promised money for their services. the first form of credit i can imagine. no one
needs money. i consider it a pointless item that increases greed. but, it is necessary. and money can be but on hold if need be. it occurred in WWII, granted its a much later period of time. people are willing to sacrifice ANYTHING for what they believe in. and if they believe strongly enough, then they'll die for it. The Crusades are a perfect example, especially the later ones, and the Child's Crusade. a blockade can stop anything it wants. if people believe that they don't need the money, then they don't need the money. and that will defeat any blockade any day of the week... except christmas.
Second, if you want the USN to stand a fighting chance in the '80s or '90s, you'll need it to have some ships to fight with. The OTL USN would be shafted. USS Texas wasn't commissioned until 1895! In fact, by the start of '96, the USN had 3 battleships, two tiny: Texas (c.6k tons), Maine (c.7k tons) and Indiana (c. 11.7k tons). The RN has about 20 battleships, all of at least 10k tons. And many many support ships.
In the Battle of New Orleans, the USN was outdated, out numbered, and out gunned. the only thing that we had was a will. and we won. the numbers don't matter when the heart is thrown into the battle. besides. whose to say there wouldn't be a saboteur? or, even consider this... a row-boat. unlikely right? well think of this, the USS Cole was attacked by a suicide bomber in a small fishing boat. A SMALL FISHING BOAT. i can guarantee that some americans would have thought of that and, during the cover of the darkness, quietly rowed to any British ship, light a powder keg, and destroyed, if not severely damaged, any of the ships. one keg would probably end up putting a small hole in there. two, a bigger hole, and three, possible enough explosives to ignite the ships actual Keg room. this would result in a similar explosion to the one that may or may not have destroyed the
USS Maine.
Third, if the French get involved - and they'd have both a) to have avoided their OTL crushing defeat in the F-P War of '70-71 to have the daring to risk annoying Britain, and b) changed their government, because old Napoleon was very keen on not annoying the British - unlike his famous forebear - then they're definitely a way to break or weaken the blockade, since more RN units'll have to be assigned to cover them.
and i said this before... its not during the late 19th century, but during the late 18th century. the French,Spanish, Dutch, and some German Mercenaries were already at war with the British and fighting for the American's independence. and the Americans would have happily given Quebec, if won, to the French. The logistics make sense. it all makes sense. just open up your mind and consider the possibilities. now, i promise that a Revolutionary invasion of Canada would be Bloody, possibly as Bloody as the Civil War. but it would have been won. and the Canadians quite possibly would have become intoxicated with the Patriotic and Independent spirit. and the french who would have been living in Quebec, may have risen and fought along their formerly British enemies. and that, would have made them American. An American fights alongside his old enemies to face new ones. Which is why now, America, Britain, Germany, Japan... were all allies. just imagine. forget about many of the rules and you may end up in interesting places.