Would the United States have been more successful if its War of 1812 had been fought against France and Spain instead of Britain?
Short answerYes, especially against France, because Britain would blockade the French fleet and the United States would be fighting on the stronger coalition's side.
NotesSpain was fighting alongside Britain against Napoleon, so the plausible American target in this scenario is France rather than a combined Franco-Spanish enemy. The Royal Navy's blockade would greatly reduce the chance that French naval forces could interfere with American operations. The United States would therefore fight alongside British sea power instead of confronting it. Participation might also earn something in the eventual peace settlement, although no particular territorial or diplomatic gain is proposed.