Under US law, the second sector is the same as the first. To be clear: the baggage allowance for the marketing carrier of the first segment is the baggage allowance for all segments of that ticket (note: ticket, not PNR). Thus, LAX-PVG (whether HKG is a connection or stopover) is the same baggage allowance.

PVG-CAN is a separate ticket four days later. The allowance for that ticket is whatever the published allowance is for that separate ticket.