21 June. International day of Music. On the longest day of the year, music festivals are held in every town in France, as well as 120 other countries.
14 July. Fireworks in Carcassonne. Over 700 thousand visitors come to watch this yearly spectacle. See http://www.citedecarcassonne.org/feux-14-juillet-a-carcassonne/
~12-20 July. Nine day jazz festival in Sete. Attracts thousands of people every year. https://www.jazzasete.com/
July. Tour de France. This greatest of all bicycle races often makes a stop in one of the cities along the Canal Du Midi, in particular Carcassonne (probably because its castle makes for nice aerial footage for broadcast around the world). Check here to see if the tour is planning to come to your overnight rest stop: https://www.letour.fr/en/
~15 August. Feria in Beziers. Five day festival centered around bull fighting. Biggest festival in Beziers. Up to 300 thousand visitors attend every year. For exact dates check http://www.arenes-de-beziers.com/