Hi,
Following is my understanding about your scenario.
Since provider link is an l3 link.your topology will be as follows.
Cisco 6509 (stand alone or VSS) --->192.168.1.0/30(provider/Cisco segment)-------provider cloud------->192.168.1.4/30-----Juniper EX 4200 (This is for one link)
Similar, setup will be there for secondary link as well.
If above scenario is correct, then ospf with authentication you may use for dynamic routing and failover to acheive your requirements.
If your links are l2, then following will be the scenario.
Cisco 6509 (stand alone or VSS) 192.168.1.1/30(provider/Cisco segment)-------provider cloud------->192.168.1.2/30 Juniper EX 4200 (This is for one link)
similar setup will be there for secondary link.
In this scenario, you may do lacp based aggregation where you may configure port channel on Cisco 6500 and ae config on Juniper ex 4200.