"sympathy deteriorated because the undisciplined Americans were often drunk and disorderly..."


This is oversimplified.   

There were many other factors in the Americans' defeat.   Especially important was the fact that the British government was enlightened enough, especially under Carleton, to treat the French Canadian culture--and religion--with respect.   On the other hand "anti-Papist" feeling ran high in New England. Many Yankees had already fought the French Canadians in the French and and Indian War and had no respect for Catholicism-- sometimes had celebrations mocking it, in Boston, for instance.    So the French Canadians did not anticipate better treatment by joining the Americans.

Also the Americans were forced to attack before the end of 1775--since many enlistments ran out at the end of the year--though this was not the best time (to put it mildly).