Guyane Evasion is a licensed receptive agency — Atout France IM973160001 — on the route des Plages at Rémire-Montjoly, putting together circuits and packages that bundle accommodation, transport, meals and activities. They sell half-day excursions as readily as two-week itineraries.
Like the other agencies here, they do not run most of the trips themselves; they book the operators who do, which is worth knowing if you would rather deal with the boatman directly.