Much more info available on Guatemala (and Bz,Hond,ES, and Chiapas) now!!!
Mayan White Water
. November better. There may be boats available,but not like Costa Rica ,Valles, or Jalcomulco.( Best bets would be in La Ceiba/ Las Mangas,Hond.( on the Cangrejal ),Lanquin or Antigua ,Guatemala.)However,it will be much cheaper to travel (maybe not to boat ),more adventurous by far,and more culturally interesting .
If you will be in Arizona anyway ,you might check into the Copper Canyon area; SierraRios: Kayak, Raft, and Protect Rivers in Mexico and Peru
. not sure on the season. Rocky is working on having boats available at different places in Mexico. Hopefully Chiapas is one of them.Tuxtla would be most centrally located and the biggest city.If you could get a boat there Tapachula is surrounded by IV- to V- runs,hair to explore higher up,play spots in town ,and the ocean 1/2 hour away. There are many 3-5 rivers to explore up the coast.
If you want to maximize your boating time it is hard to beat Costa Rica,Ecuador,or the popular areas of Mexico (Boquete, Panama too). Driving all the way to South America is an ordeal.