The pivotal victory in the French-Indian War, was the Battle of Quebec. The French held Quebec (today Quebec City), which was perfectly situated to protect use of the St. Lawrence River. French control of the river made it extremely difficult for the British to get forces and supplies deep into the Canadian interior, as they had to detour through the colonies on overland routes that were frequently closed by snow during the winter.
The British capture of Quebec opened the river to British naval traffic, and closed it to the French. This allowed the British to get forces and supplies deep into the Canadian Interior, and overwhelm the Indian tribes who had sided with the French. The French were unable to keep up with their remaining access through the Mississippi River, and were forced to concede Canada to the British.