Not a single pre-columbian city in the americas had a million people.
In North America, the largest city, Cahokia, had 15,000 - 20,000 and peaked around 1100 AD. North America was mostly a stone age culture without a lot of cities.
You had more advanced civilizations in central and south america.
The Aztecs were the biggest. The largest urban area were the two sister cities of Tenochtitlan and Tlatelolco. Again, population estimates are hard to come by, but 200,000–400,000 inhabitants are estimated for Tenochtitlan and half that for Tlatelolco. https://en.wikipedia.org/wiki/Tenochtitlan
Teotihuacan was the largest city in the Americas during the classical period, beginning to decline around 600 AD and virtually dissapearing by 1000 AD. Peak population of 150-250,000 around 450 AD. https://en.wikipedia.org/wiki/Teotihuacan
The absolutely fascinating Olmecs (with the enormous heads and jade masks), were the largest before then, but they died out around 450 AD. https://en.wikipedia.org/wiki/Olmecs
Population estimates for their biggest city, La Venta, are about 20,000 people.
Teotihuacan had about 125K around 500 A.D, but again collapsed by around 1000 AD.
In South America, the largest Incan city, Cusco, had a peak population of up to 150,000.
https://www.worldhistory.org/Cuzco/
Tikal, the largest Mayan city, had about 200,000 (Peaking around 900 A.D)
Etc