Not sure about Cayenne as i didn't go in there, got couple hundred litres in Kourou but meant a long wobbly bike ride up to the filling station with jerry cans. Not cheap
either. Surinam was a nicer place, though Isle Du DSalut were beautiful. Noonsite says fuel
available up the river, I remember going past it but didn't get any.
Domburg. domburg suriname - Google Maps
Domburg is the place to go for in Suriname, a few hours up the river. Lots of Dutch. Great food
Where in Brasil are you?