Regarding Spain, the OTL assassination attempt happened roughly around the time that the Anglo-Spanish-Portuguese forces started to suffer a series of setbacks, such that the French (as they did OTL) could easily push back the British out of most of Spain and into Portugal proper; depending on if the Peninsular War continues for another couple of months or years, the French could certainly reclaim "Joseph's" country, and maybe even retake Portugal (but only if they used a significant fraction of what was used for Russia OTL). AAR, I'd say that a final peace with Britain would likely include Joseph getting Spain, Portugal remaining an independent British ally, and the islands and sea power in general basically being given to Britain... and, of course, ending the blockades.
Britain likely wouldn't cotton to having a Bonaparte commanding the Spanish Empire in Latin America; fortunately, they have been supporting independence and autonimist juntas in the Western Hemisphere, plus France still has possession of Ferdinand. So I'm seeing an endgame here where Britain agrees to let Joseph keep the crown of European Spain, while the Spanish Bourbons cross the Atlantic and Latin America's break with Spain comes several years earlier than OTL. Thoughts?
And something else I just thought of -- would the US still see the election of the war hawks in 1810, and subsequent declaration of war against Great Britain? And if Britain isn't distracted by the War of the Sixth Coalition, and possibly even having reached accord with the French over Spain, will the Americans now do significantly worse? And what does that mean subsequently for North America?