I'm not convinced that this will work but a few more details are required:
When a VPN client connects and is allocated an IP address of 10.55.55.x - what is that client trying to connect to? A 10.66.66.x address? Or a 172.17.0.x address?
You mentioned that you've added routes in region B but have you also added the "opposite" routes in region A? Routing is a two-way process - adding the routes in one direction doesn't automatically make it work the other way around for return traffic.
I redid this with a whole 10.66.0.0/16 network and then put 10.66.66.0/24 on the VPN side and still the destination isn't getting routed through the Peering when I point it to the 10.66.0.2 adapter. I am convinced Peering isn't working and this is a bug.
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