https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/gi-036/beverages.html
Carbonated beverages
Carbonated beverages are taxable regardless of serving size or packaging format. Examples include carbonated soft drinks, mixers such as tonic and soda water, carbonated mineral water, sparkling water, carbonated juices, and non-alcoholic malt beverages.
Many establishments operate soda fountains. These fountains are operated with cylinders of pre-mix or post-mix. Pre-mix is a carbonated beverage. It is supplied in a cylinder and contains all the syrups and CO2 required. The operator attaches this to the fountain and the fountain dispenses a carbonated beverage. Pre-mix acquired by such establishments is taxable. Post-mix contains other ingredients for a carbonated beverage but does not contain CO2. Post-mix is zero-rated.