I was reading "The Opium Wars: Drugs, Dreams and the Making of Modern China" by Julia Lovell.

In it, she discusses the nature of the defensive preparations Canton was equipped with at the dawn of the conflict.

The canon defending the Canton forts were a little outdated. They were not swivel mounted or sighted, two factors that diminished accuracy. Once you were out of a particular pieces line of sight, that canon was useless as it could not be easily adjusted to another position. Qing war junks carried about 10 guns each compared to the hundred + gun ships in the British fleet of the time. They were smaller vessels too, and not as sturdy sailing as the copper lined hulls of the British ships proved to be, and almost useless unless in calm waters. The lack of good fighting ships to counter the British essentially let the British pick the time and place of the attack, and once out of range of a particular Qing fort, the ships were pretty unassailable.

Some of their forts were well constructed of stone, strong material and tall thick walls, but roofless. This flaw made their occupants especially vulnerable to mortar attacks from the British vessels. The forts were more designed to prevent/deter piracy (the main source of sea attack that Canton was preparing for) but little thought was given to shoring them up from land attack. As a consequence, the forts utility was further undermined by their vulnerability to land attack, something the British took advantage of during the campaign.

Lastly, the nature of the Chinese military at the time placed the Qing dynasty at a disadvantage. Throughout the course of the 18th and 19th century, training in the use of musket, canon and other implements of war decreased as the cost of ammunition was dear. Furthermore, there was corruption in the rolls. One Imperial Representative at Tianjin recorded that of the 2400 men theoretically enlisted and collecting rations, supply and pay, only 600 could be mustered. The speed of their deployment was also at issue. While neighboring provinces could supply reinforcements to Canton in 30-45 days, the author mentions that this is the same amount of time it took for the British to resupply Canton from India. More distantly deployed reinforcements took months longer to make the trip.

As for the Eight Banners system, the book has some information which highlights that the Manchu in charge of Qing China were themselves foreigners. A watered down system of the Confucian Civil Service exam existed solely for Manchu's while non Manchu Chinese had to take the 'real deal' version of the exams. This had a two pronged effect. On the one hand, the Manchu given preferential treatment by this system wasn't always the most qualified for the job, and secondly, the non Manchu's hated the fact that Manchu's received preferential treatment. The trade off was supposed to have been that the Manchu official would know other useful skills, archery, horsemanship, Manchu skills that helped them conquer and hold China together. But many had taken to the role of bureaucrat with elan and let slide the military aspect of their civic responsibility.