The victory at Quebec can be attributed to many factors. Although Quebec was heavily defended, the overall position of the French was extremely weak. They had lost many of their Indian allies. The army was strained to the limit after years of fighting against the greater resources of the British. British victories at Fort Duquesne and Niagara cut off French communication with the west, leaving the forces at Quebec without reinforcements of either men or supplies. All of this combined with James Wolfe's tactics of terror made the siege brutally effective.
It helped that Quebec's landscape was not twisted and wild like America's. The British soldiers could exercise their disciplined techniques of columns and volley fire without the threat of sniping and ambush that had worked so well for the French in the American colonies. Wolfe was also fortunate to be aided by several unflappable and highly skilled officers, including Saunders, who held up the pillars of the final battle.
After the fall of Quebec, the rest of the war was almost an afterthought. The French forces had been completely demoralized by a string of defeats, and the British were in position to dominate both the West and Canada. After a feeble attempt to win back Quebec, and a brave attempt to hold out against the British at Montreal, the French capitulated and turned their attention to gaining the best treaty possible.