How would things be different if the American Revolution had never happened?

Counterfactuals can be difficult because it is rare that the occurrence or non-occurrence of an event will lead to one specific outcome. It is impossible to say what the world would be like without the American Revolution, both because it happened and, therefore, colors our judgement, and because the non-occurrence of the American Revolution could have led to various differing outcomes.
One potential outcome is that North America may have remained under the power of England, France, and Spain into the present day. Without the American Revolution as a successful precedent, the Mexican Revolution may never have occurred. This is unlikely but possible. Without the Mexican Revolution there is a possibility that Spain, although on the decline, could have retained its holdings in Florida and South and Central America (as well as the Southwest of North America). Similarly, without the American Revolution the French Revolution may not have occurred. The American Revolution served as a successful precedent and gave the French Revolutionaries some hope, while the French role in the American Revolution worsened the country's economic issues and provided fuel for the Revolutionary fire. Without the French Revolution and the near bankruptcy caused by supporting the Americans, the French would likely have retained their control over the Central US.
Canada's eventual independence makes it unlikely that England would have retained control over North America indefinitely. The American colonies could have gained independence at the same time as Canada, though it is likely that the New England colonies would have joined Canada. The Middle and Southern colonies could have united into one country, or formed several countries. If this occurred then the eventual decolonization of North America (after it became a sufficient resource dump) could have led to the enlargement of Canada, or the emergence of additional small nations governed by Native Americans or by other settler groups. These are just some possibilities.