3 networks/subnets question

I am looking for some guidance setting up the following:

I have three networks:
A : 192.168.21.0/24 192.168.21.1 is untangle 10.1; 192.168.21.2 is CISCO for T1
B : 192.168.3.0/24 192.168.3.2 is CISCO for T1
C : 192.168.8.0/24 192.168.8.1 is untangle

A and B are connected with a dedicated T1 circuit.
A and C are connected using the OpenVPN module in Untangle.

Communication is working A to B and A to C.

Is it possible for B and C to "see" each other? What do I need to do to set this up?