Thanks very much for your replies, everyone.

Yes, the reason I am taking the flight ex-YYZ on CX is purely for Award availability - that's where my miles are, and there was nothing out of JFK direct to HKG.

It also means I can connect with the 1:30am CX departure, getting me into HKG in the morning rather than late in the day.

It sounds like I should try to hang onto my bag LGA-YYZ so that I don't have to check it until I get to the CX desks at Terminal 3; that might help with the stress levels.

Thank you again for your help.