Why is roman catholic the main religion in Brazil?

Because Brazil was originally controlled by Portugal, a Catholic country.

(Historically) Catholic European countries include (but are not limited to: ) Spain, Portugal, Italy, France, Austria, Luxembourg, the Republic of Ireland etc. By contrast, England, Germany, Scandinavian countries are Protestant.

In the United States and Canada, a lot of people from historically Catholic have immigrated there so they are becoming less Protestant. (Note that Quebec province of Canada, being a French Colony, was always Catholic).

In the new world, the majority religion of countries is largely controlled by what European power originally colonized it.