Millions? I don't think so. Maybe a few thousands? I think you overestimate the amount of people in Brazil who fancy a life in the US. Furthermore, I also think you overestimate the amount of people who, fancying a life in the US, are actually able to secure financial and social resources to move there.
Brazilians have visa-free access to Europe[0] and you don't see "millions of Brazilians" just going there and staying. Why would it be different?
[0] Technically there's a visa which is granted on arrival