I am afraid that if you are incoming from YYZ or YVR on CX Biz Class and then on MU flight to China , CX lounge staff in HKG will not allow u into their lounge.

As for incoming from CX long haul flight Biz class (Rev or award)ticket and then onto a KA flight Economy class (same day connection) CX will allow you to use the CX lounge in HKG.