New France faces four large obstacles to its survival, let alone victory:
1) Population. As of 1754 the population of New France was roughly 70,000. Add to that another two thousand or so friendly Indians. The English colonies at the same time had a population of nearly one million. The New French are outnumbered almost 15 to 1; not good odds.
2) Resources. New France imported almost every necessity, not excepting food in some years. In contrast the thirteen colonies were essentially self-sufficient. If supply from France is interrupted for any length of time the New French will quickly begin to run out of essential materials, while such interruption would only be a nuisance for the English.
3) The Royal Navy. The French Navy is no match for the British, either in quantity or quality. The British could shut off the flow of supplies and reinforcements to New France whenever it suited them to do so. They could also bring sufficient force to bear to seize any point in New France whenever they chose to do so.
4) The French administration. New France was often neglected in favor of the more profitable French West Indian islands, just as the French navy was often neglected in favor of the army.
New France might overcome one of those obstacles, or maybe two. All four together mean that New France is doomed the moment the British decide to take it.