This is not a exhaustive list of treasures per region, but I want to give share some perspective: there are way more than 200 treasures in the game so you'll be able to get the achievement even if you miss a few. There's no achievement for opening every single treasure.
For reference I got the achievement for opening 100 treasures before finishing Act 2.
When you collect 5 Li'l Cactus as a reward your map displays how many treasures are on the region. It doesn't show where they are, but it tells you how many to look for. I found it helpful for exploring.