I think a more basic question is why are you using VSTP in the first place? I assume Edge is Cisco, and MDF now Juniper? Even then just get rid of VSTP on Cisco and make the dual links A/A FEC and connect to the Juniper Core via a LAG/AE.
STP of any sort should not be a requirement of 95+% of networks build past 2010.
My 2 cents worth.