The closest boating to DF is the Amacuzac near Cuernavaca and Taxco apx. 2 1/2 hrs.There are some rafting outfitters,google Rafting en Morelos,but their site wasn't very helpful.I think it is III - IV ,don't know the season,check 'Grigo's Guide to Mexican Whitewter'.
Veracruz is a much better bet apx. 4 to 5 hrs. by bus,costs about $40 for deluxe bus to Jalapa,they should be able to get boat under the bus if it's short.If you don't have a boat Jalcomulco is the best place to find one to rent,maybe Tlapocoyan or Micos camp,but Micos is farther 6 1/2 hrs. might be optimistic .An overnight bus can get you to Agua Azul/Palenque or Huatulco/Zimatan-Copalita rivers.Agua Azul is f#%$ 'n awesome and almost always has water,you could do it yourself just scout the drops you like and huck away,give yourself more time than the daytrips from Palenque allow,there is a lot to scout and you wont want to leave,best is to go to the ruins early ,get out to AA in the afternoon scout/huck a little then stay out there and awaken with kayak disneyland at your doorstep.
The Oaxaca coast has good beaches and surf if the rivers are'nt running.
I really like Mexico City,but it's not everyones cup of tea,if you like history,archeology,art, and good food it kicks ass.Recommended; Teotihuacan,Museo Nacional de Antropologia,and Zocalo/Natl.Palace w/Rivera murals.also exhibit on the instruments of pain and torture of the Spanish Inquisition[was in the Escuela de Medicina].Have fun ,especially if you are driving in that madhouse!