If I follow your setup correctly that the L3 interface on the PAN needs to failover between active/passive units to the QFX.
I would use an irb interface assigned to the vlan. Then have the two PAN connected to ports in that VLAN on different members of the virtual chassis.
This way failures of either a single QFX member or the PAN active would still work as expected.
------------------------------
Steve Puluka BSEET - Juniper Ambassador
IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
http://puluka.com/home------------------------------