I visited Guangzhou and there are many halal restaurants there .They even had halal restaurants at airport. Xiaobei Road has many halal restaurants and shops and is the most famous area for halal food.

Salaam I've been to China and Japan. China has 2-3 halal restaurants in every food court of 10 in the cities but outside the cities they eat pork in everything even vegetarian food.  Japan was hard to get halal. We ate vegetarian and fish a lot. Getting around in China we flew it was cheap but the country is too vast to do anything else. Japan has bullet trains and it's very easy to get around. Chinese people don't speak much English. The Japanese are much better. Get an eSIM at the airport and use Google translate.