My daughters have dual citizenship. The schools in the US cared that they are a US citizen but did not care at all about their Canadian citizenship. The schools in Canada cared that they are a Canadian citizen but did not care at all about their US citizenship.
One issue is that if you complete high school in Brazil you will be out of state for probably every public university in the US even if you are a US citizen.
Most of the scholarships at US schools will come from the schools themselves. Some are need based. Some are merit based. Frequently you won’t know how much a school will cost until you get the offer of admission, but you can get a good guess from the Net Price Calculator. If you google " net price calculator" you should be able to find this.
We never found any scholarship that cared about the fact that they are dual citizens.