https://easc.osu.edu/resources/k-12/lesson-plans
This resource site provides a bank of lesson plans coordinated by the East Asian Studies Center and National Consortium for Teaching About Asia programs. Lesson plans are categorized by China, Japan, Korea, and East Asia in the categories of:
Art & Architecture, Culture, Economics, Education, General, Geography, History, Language, Literature, Politics, and Religion.
If you are looking to find resources that compares side by side these three countries, the fourth category--East Asia--is also a great source. I will definitely use this resource when planning a comparative literature unit with my ELA students. Since I can already find a category on literature, I can look for stories specific to each culture. If I wanted to have discussions about art, I can look at Art & Architecture.