The movie theatre chain says drink sizes will simply shift downward: the large drink will go from 44 ounces to 32 ounces and the regular drink size will go from 32 ounces to 24 ounces. The small will stay at 16 ounces.
All beverage prices will remain the same.
Toronto-based Cineplex says it's part of a countrywide reduction in cup sizes.
Cineplex has been testing the revised drink sizes in British Columbia and Saskatchewan since 2013. The smaller sizes are moving across the country.
"Because we found a general trend toward smaller cup sizes, we made the choice to reduce the size rather than increase the price," company spokesman Michael Langdon said.
Langdon added that Ontario's Making Healthier Choices Act, set to be introduced in 2017, also factored into the decision.
The Act will require fast-food chains to display calorie counts on their menus, unmasking just how much its biggest drinks count towards your daily intake.
"We're making a change to help prepare for that," he said.