southshorecanopy.com in Roatan.
$65 each. Met them at 8am went right up, we were back at the pier by 9:45.
Personally, I hated it. But then I'm scared of heights and I figured that would happen anyway. But my wife loved it, and she's in charge, and we did my horse riding in Belize, so I did that for her.
I bought the "survivor" t-shirt at the end, and within 24 hours my legs stopped shaking. If pretending you're a baboon is your thing, then do it. Tell Therise "hi" for me. They were very nice about me being petrified.
In Belize, for cave tubing, do cave-tubing.com. Unless you'd rather spend about twice as much, and have half the trip and a third of the fun.
The Carnival-offered excursion puts you into the river halfway up, and just tells you to head downstream. You can't get lost, but people are bumping into everything along the way and getting stuck in shallows in dark caves... And they charge you more to let you fend for yourself.
The cave-tubing folks take you farther upstream, let you dive into a deep pool if you wish, then form a chain and lead you down around all the Carnival schlemiels who are stuck in the shallows. Plus they feed you afterwards, and give you a shot of cashew "wine" on the bus trip up. You can buy more shots for $1.