The good news is that Mt. Ste. Victoire---one of the great crags of France, is just outside of Aix---the bad news is that it is almost totally south-facing and will be an oven in August. However a number of other areas such as Les Calanques on the coast to the south or the Verdon Gorge area in the mountains further north are within reasonable reach of Aix and, while still hot, will likely offer more options for shade and tolerable climbing conditions. As for guides, it is quite likely there are some guides based in Aix itself--try a google search. I know that Englishman Alan Carne is a guide based out of La Palud in the Verdon and there are surely others there.
My wife and I hired Guillaume Vales (www.climbout.fr) for a couple of days in 2012. His English is fluent and was a great guide for the area (based out of Marseille, he picked us up @ Avigonon -- Aix should be no problem since it's closer to Marseille). I highly recommend contacting him for hire/advice.
Sunny Yum From Boulder, CO Joined Oct 15, 2010 20 points
a number of other areas such as Les Calanques on the coast to the south or the Verdon Gorge area in the mountains further north are within reasonable reach of Aix
Actually most of the classic routes in the Calanques are S or SE or SW facing. Also at least two of the driving access roads (Sormiou + Morgiou) are closed all the time in the summer (except by special permit). And some areas of the Calanques will be closed even for walking access, because of fire hazard (some website posts a map for each day of which sectors are forbidden).
Verdon might not be that far in straight-line distance from Aix-en-Provence, but there's no simple short way to drive there. Note that inland can sometimes be hotter than the seaside, because it lacks the moderating influence of big water -- so you have to get to fairly high altitude to be assured of cool-ness. . (There are lots of other good fun inland climbing areas at higher altitude with easier friendlier access than Verdon, just not well known to Americans).
Likely the best idea is to hire a local guide for a half day of cragging (couennes), and then go swimming in the afternoon. Presumably your guide will know some suitable north- or west-facing crags.
To find a guide, try web search for "Climb Provence" or the Cassis / Calanques guides bureau / office. But most guides (who love climbing) just escape to somewhere else for the summer.