Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
AA does not offer any free stopovers on its awards. But since BA charges for each flight flown, stopping over en route costs the same number of miles as merely connecting. (Chase Sapphire Preferred points can be converted to BA Avios.) If you can find "SAAver" award space on AA flights at aa.com, you can redeem 12,000 BA Avios for OMA-DFW-CUN one way in Coach, with or without a stopover at DFW.
Google "CUN airport wiki" to find the Wikipedia article which will show all cities with nonstop service to CUN.