An aside on Burma and the Opium War of 1839-1842...
Britain fought three wars against Burma : 1826-8, 1852 and 1885. In the first war it defeated the Burmese on the coast and as a result of treaty got the Arakan and Tenasserim regions (as modeled in the start of the 1836 scenario). The 1852 conflict led to the seizure of S Burma (Rangoon-Pegu) but the Brits (actually the BEIC army) were unable to do much in the interior and that was left to the Burmese. Only in 1885 was the decision made to move into the heartland of Burma (the coastal area was historically low population until the British seized it and developed rice agriculture in the region around Rangoon) as the French were moving inland from Vietnam and the Burmese monarchy started flirting with the French as a counterweight to the British.
That British commanders would have even possibly conceived of invading China via Burma in the 19th Century is almost beyond plausible. Heavily jungled mountains with no infrastructure to speak of, the China-Burma border has historically been the dividing line between the Chinese world and the Indian-SE Asian world, only very tenuously under the control of either the Burmese state or China until only the last 10-20 years (and even now the Burmese side is still unstable). The problem to me sounds like the UK ai (soon to be Indian, since all the ideas for going to war with Burma came from Calcutta, not London) is WAY too agressive towards Burma. Never mind the point that Britain's power is historically at sea, not land. 200K Br Indian forces crossing the mountains from Upper Burma to Yunnan to invade China, not even historically feasible today, let alone the 1830s. Focus the UK ai on launching successful sea invasions at Hong Kong and Guangzhou to recreate the Opium War, not to seize all of Burma ahistorically early. Connect an event from the Opium War series to the loss of say Guangzhou or Hong Kong to the British to end the Opium War with the cession of Hong Kong (with a b-option for the UK to refuse the treaty and continue so that human players can go on and conquer if they wish.) The Opium War was NOT in the British view about conquest of China, only opening it up to free trade. With the exception of the Indian Subcontinent (agian, at the urging of Calcutta, with very gruging support and sometimes reprimand from London), Britain in general avoided wars of conquest and subjugation until the 1870s, when competition from other Europeans for access to colonial markets touched off the various "scrambles". Britain pre-1870 had no need for adding new land to its empire - its economy needed markets and the cost to administer colonies was more than the perceived benefit. As long as it had access to open markets, the British were more than content to allow non-Western states to stay independent, and if push came to shove, the most the British wanted were access points (like Hong Kong), not total conquest. This can be seen in Burma. The 1852 war was over Burmese refusal to open trade. War was fought, it was a hard fight but one the British could have won if they had wanted to, but in the end decided only to take the coastal south, with its low population and easy sea access. The Burmese heartland, heavily populated, would have become yet another drain on the British E India Co's already stretched budget, so in the end the interior remained independent. Only with growing French interest in the region do the British take the final plunge and annex Upper Burma.