Hi, since no one else is answering you I'll try. I have been visiting Yellowstone for over 30 years. I'm afraid this most popular tourist destination has been destroyed by it's own fame. I doubt you will get a reservation at this late date but if you do grab it. Canyon is fine, I think Bridge Bay is better, or Grant's Village. However, all of the campsites are in touch with each other so if one is filled I think they can link to others to know where vacancies are. I never go there in the summer months anymore. I love early spring or late September or early October.
There are two loops to drive in the park, sort of like a figure 8 - I would suggest you set at least one day aside for each drive. Then if you want to hike into some sights you may have to plan from your main campsite and allow even more time.
Be sure to search out Artist's Point (commonly referred to as the Grand Canyon of the Yellowstone). Everyone finds Old Faithful but many of my friends come home having not seen this sight.
Good luck. Enjoy! The park is a fascinating experience.