I think August is the best moment for visiting.
Si le temps est meilleur qu'il ne l'est actuellement... (If the weather becomes better than currently... )
Lynn 007: I'm glad you liked the idea
Actually, this is quite difficult sometimes to find a place without tourists in a city like Paris (especially when someone doesn't know this town) but la promenade plantée is one of them.
This is nice to discover the city from another view, and, at the same time, to take a ride for free in a beautiful & vegetable way.
By the way about veganism, like Olivier said, don't worry. Actually, Paris is surely the best city in France for vegans, because it's quite "big & famous", so there are some shops especially for vegans. (I'm not so I'm not perfectly sure, haha, but I guess n_n)