Arnold's trek through the Maine woods was a disaster. Likewise, the boat trip down the Chaudiere, which was not known to be a white water river.
At least Richard Montgomery and his forces came by water, which made them battle ready.
Montgomery and Campbell got killed at the east gate of Quebec. Burr tried placing his people in the buildings as snipers only to discover that Sir Guy Carleton had gotten the same idea.
At the west gate, Arnold and Morgan pulled off two valiant charges with the result that the British troops were on the edge of panic and ready to flee. Arnold's wounding prevented a third charge, which would have taken the city.
The future Lord Dorchester's career would have ended badly that day with one more charge.
Quite true.
However, even had they taken Quebec I doubt they could have held it. They were getting into imperial overstretch without even having been an empire. The British could bring in tropps up the St. Lawrence more easily than the Patriots could up the Champlain.
The French Canadians were just never going to be enthusiastic supporters of the American Revolution. Their Catholic and feudal orientation was just too different. At this point in time there were essentially no “English Canadians.” In fact, the first English Canadians were mostly American Tory refugees from Patriot persecution.