We try to avoid AK all together at the hottest times of the day. I swear they pump heat into that place.. and other than maybe Festival of LK, there is no where to stay cool.
At MK, some good choices are HoPres, CBJ or PhilharMagic.
For EPCOT, we always head to either UnivofEnergy or the Land/Soarin (where you can also sit and get a snack in the nice cool a/c)
At MGM, you might want to check out the GMR or MV3-D
all of the above options give you a good amount of time to cool off inside a/c buildings... and many of the lines for these attractions are indoors as well -- an added bonus!