I think that an open and free China would still have many of the same geopolitical incentives that authoritarian China does. It would still prefer to dominate global manufacturing, use its resources and manufacturing capabilities for geopolitical leverage, and militarily dominate the seas and islands in its vicinity. It would still be nationalist. It would still want to reverse the "century of humiliation".

Type of government does have an effect on economic and military policy, but being a liberal democracy does not make automatically make a country less interested in pursuing naked self-interest.

It would simply be a larger more powerful south korea (well not exactly since china actually has resources vs south korea).