Final answer:
The city on Guanabara Bay in Brazil is Rio de Janeiro, known for its significant population, cultural attractions, and history as a former capital.
Step-by-step explanation:
The city that lies on Guanabara Bay in Brazil is Rio de Janeiro. Rio de Janeiro is not only a major travel and international business center with a population of more than 10 million, but it is also noted for its dynamic carnival festivities and its status as an industrial hub. The city's cultural attractions and renowned coastline make it a popular destination for tourists, and its history as a former capital before the creation of the forward capital of Brasilia highlights its importance in Brazil's development.