maybe Salto de Eyipantla?
Honestly I haven't seen the movie, so I can't confirm this is it, but I do know that the film was shot in the regions of Los Tuxtlas (Catemaco/ San Andres Tuxtla) and Paso de Ovejas, which are both quite aways away from Tlapacoyan and Tomata and all that. The most famous and accessible waterfall in Los Tuxtlas is called "El Salto de Eyipantla" but there are definitely other waterfalls in the region. Google it and see if it matches the one in the movie. Thats my bet.
I've been to Los Tuxtlas and Catemaco (side note: Catemaco is considered the "brujeria" (witchcraft/witch doctors) capital of Mexico-- kinda adds to the already surreal atmosphere there). As I'm sure you saw in the movie, there are a lot of rivers, lakes, mountains in the area, much of which is some sort of nature preserve that covers much of the region. Its a beautiful mountainous rain forest area that borders the coast; full of rivers and creeks, with some definitely first D's to be done in there. I've never really heard of anyone kayaking in that area, although its probably been done-- I haven't been in the kayaking scene very long or paid attention to every expedition or first D in Mexico. Los Tuxtlas is a long ways from the Filos, Antigua, Actopan, Alsaseca and other rivers close to Xalapa, Orizaba, and Veracruz that you think about when you think of kayaking Veracruz and is actually in a completely different mountain range several hours to the south east of those places.
Waking up in a hotel on Lake Catemaco to see fisherman in wooden canoes casting their homemade nets across the misty mountain lake with lush hills rising all our around is an absolutely surreal memory for me. The region is as backwards and poor as Mexico gets; much more so than the areas closer to Xalapa and Veracruz (city) such as Tlapacoyan, Tezuitlan, Martinez, Orizaba, etc. Veracruzanos in general (colloquially known as jarochos) often prove themselves to be the most friendly, easy going people in all of Mexico.