Cancún is a city, not a sovereign entity. It has no independent government.
Benito Juárez municipality covers Cancún + surrounding communities (Puerto Morelos, Alfredo V. Bonfil, etc.). Quintana Roo state government handles education, health, state police, major infrastructure.
Tourism decisions (zoning, permits, beach access) are municipal. Security = municipal police + state police + National Guard. Taxes = federal (SAT) + state + municipal (predial).
Cancún runs on municipal ordinances within a federal system—not its own "government."