First point: beg to differ, you will get J lounge access at YVR based on CX's (rather generous) in house policy:

https:/www.cathaypacific.com/cx/en_HK/destinations/lounges/all-lounges-admittance.html

"If you're travelling on Cathay Pacific operated flights in different cabin classes within the same journey, you can enjoy lounge access if at least one sector of your journey is booked in First or Business class, and your connection is within 24 hours. We will honour the highest class of travel for lounge entitlement* throughout the same journey to ensure maximum comfort. In cases where the journey includes a stopover, lounge entitlement will be honoured based on individual sectors."

Can't find anything official from CX w.r.t. check in & boarding priority - it doesn't make a difference for non-DM status pax - just hazarding a guess, YMMV for priority check in but probably not for priority boarding?