The war of 1812 effectively was the US entering the war.
This. The USA declared war against the United Kingdom, thus being
de facto allied to Napoleon. It didn't change history very much (except in the development of Canadian nationalism); there were a few battles that went each way, and then both sides decided not to bother fighting any more and gave up without changing anything. (Except for the UK betraying its Native American allies as soon as it was convenient to do so, but that was nothing new either.)
If you mean the USA intervening
directly in the French Revolutionary Wars, which took place in Europe… no. Even if the USA had the inclination to intervene, it couldn't project any noticeable amount of power in Europe.
{edit} And even in North America, if either France or Britain hadn't been distracted by constant wars against the other, either of them had the power to crush the United States like a bug underfoot. One mustn't confuse the USA of the 1860s with the USA of the 1810s; the former could have been reasonably significant on the world scale had it chosen to be, whereas the latter could not.