Venezuela has the same problem. Due to the jungle in that area, they would be forced to go through Brazil to get to Guyana in the first place.
Brazil is simply moving their forces into the extreme North of Brazil as that is the only realistic access to Guyana for Venezuela due to the jungle on the border of Venezuela and Guyana.
Not sure if it’s true, but it was the analysis I read last week when this issue was being discussed.
Brazil announced that they’re moving their army to the north, but I believe their politicians are all stupid and would announce it even if they are not capable of moving heavy weapons there.