AIS has published a list of the worldwide roaming partners. While updated infrequently, it will give a rough idea of the network your eSIM2fly will be connected to in each country. Multiple carriers in each country mean any of them will work.
Manual Network Setting
AIS does make it is possible to manually select your network. If you find you are in a location and your network choice is switching between carriers or not connecting, you can do a manual network selection.
Go to Settings > Cellular > Network Selection.
Countries and networks covered by the AIS 4G Data Roaming service
AIS is a member of Bridge Alliance and together with the Bridge partnership, AIS will roam with any of these partners. Mostly focused on Asia, this is a partnership of Asian telecom companies. This means and AIS eSIM2Fly will roam on either China Telecom or China Unicom in China – whichever is available and preferred. Other notable carriers include Softbank Japan, SK Korea, Singtel Singapore and Airtel India.