Avenue de Champage - pre-booking required

Hi. On April 18th we will have a single afternoon available for Avenue de Champagne in Epernay. We arrive in Reims at 11:30. Once we store luggage we will take a train to Epernay. Must I pre-book Champagne tastings on Avenue de Champagne or can we just show up? I have a tour and tasting booked for Mumm in Reims the next day but would like the option of being more spontaneous as we stroll Avenue de Champagne.