The French, Dutch and Spanish navies combined proved incapable of defeating the British and the latter could therefore pick off colonies at will. Prussia had no significant navy to add to this equation. Without naval superiority Napoleons only hope of defeating the British was the Continental System and he had no soft power methods available to get half of Europe to play along.
Napolean had bigger troubles than the Britons. The combined armies of Prussia, Austria and Russia are superior to the French army. To his luck the three land based majors were unable to coordinate their efforts till 1813 therefore they could defeat them in details, but at an ever increasing cost.
France needs either Austria or Prussia as an ally.