Good morning;
Others have covered the cameras; I will address a backpack for cameras.
You spoke of compartmentalization and the need for carrying a laptop computer. For that combination, I use a Lowe-Pro Compu Treker Plus AW. Yes, it is large, but that comes along with the space for the computer. That extra space can also be used for clothing and other things. As a pack, it also fits and functions fairly well for me, but the Lowe-Pro people have been making backpacks for years, so that is not really a surprise. The waistbelt is not quite the equal of my Gregory Denali-Pro, but it certainly does put the weight where it should be for me. Dan McHale may be one of the few people who could improve on Wayne Gregory's design and fit, but then, Dan does only custom made and fitted packs.
LowePro does have an office in Markham, Ontario (905-944-9400), and many photo shops carry their products.
When you return, please share with us the story and photographs of your trip to China.