I suppose it would help to know what you already know. But I would say the Oxford History of the United States is pretty good, what has been released yet. I thought American Colonies by Alan Taylor was pretty good as it does cover Mexico and Canada in part but it does focus more on the US. Also have read A Concise History of Canada and started to read A Concise History of the Caribbean which are good starts to topic but challenging. An Indigenous People's History to the United States by Roxanne Dunbar-Ortiz is good too. Good Luck would be cool to see a more continental approach to NA history.