Given the architecture, I expect the samba roadblock to be somewhere in the Santa Teresa neighborhood. That would also fit in with the teams having to take the tram. If anyone has time to look for the location, that's where I would start.
The following is only spec.
In terms of the pitstop being in Niteroi, it seems to me that the only reason would be to have it be at the Museum of Contemporary Art
which has amazing views of Rio. They will need to cross over the bridge to get there, but once they arrive, there is a huge ramp going up to the main building. It's very stage-ending worthy.