Cisco WAN :: 6509 - L2 Etherchannel Over 2 ISPs Between Two Sites

We are implementing the network design between the two sites (OLD Data center and NEW Data Center), scheme in attachement.
 
We have chosen this scheme on the following criteria:
- A single IP network between the sites (for simplicity migration);
- Fault tolerance via different ISPs.
 
But the problem is L2 etherchannel doesn't work correctly: When one side port is shutting down, on the other side etherchannel will not rebuild and does not see that link down on the other end. We have tried to use LACP in etherchannel (mode active on ports), but result was the same. Is it on the ISPs side?
 
Should we use this design or we have to subneting the network and make connections between the data centers classically with L3 channels and OSPF?

The configures of Core ports listed below:

OLD data center core (Cat 6509):
 
interface GigabitEthernet2/6
description #### TO DATA-CENTER core 1#####
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport mode trunk
logging event link-status