Loca Pirogue has been hiring out boats on the rivers around Cayenne since 2004: motorised pirogues, kayaks, paddleboards, and the kit you need for a night in a carbet. They work with individuals and with companies, and quote per trip rather than off a price list.
They are on the RN2 south of Cayenne, in Matoury, which puts them close to the Mahury and the roads inland to Roura and the Comté.