Britain is very hard to make peace with. In general the AI is heavily influenced by the relative military strength of the two combatants. The more the ratio of Military ratings is in its favor the less likely it is to make peace. Ignore the game notes for V1.03 that the AI is more likely to make peace w/China. A large power like the UK or Russia with a high military rating will be very hard to make peace with, particularly early in the game when the human player (as China or any other smaller or uncivilized nation) has a low military rating.
A good strategy for China in the first Opium war is the take your best leader with a negative attrition mod, give him a big stack of troops and seize the adjacent Indian province (Dibgarath). Then just sit there and use the defense terrain to beat back sporadic UK attacks. This will run by UK WE faster than yours and will help get a peace quicker. Use the intervening time to seize all those UK claims in places like Africa and Australia. Convert those claims into colonies and you can get civilized status fairly early.
