UC (CUCM/VOIP) over VPN may not be the optimal experience. I've only seen clients use this as a backup/fallback method if primary links (MPLS, Fiber, OC3, etc...) go down. Depending on the size of the site you may run into quality/registration issues.
Your network/VPN setup at site B needs to communicate with site A and the Voice-VLAN/CUCM network/subnet. Where is your DHCP located? It will need to be configured to provide Voice VLAN IP addresses and have at least option 150 set to point at CUCM(s) running your TFTP services.
There is probably more to configure depending on where your PSTN circuits are located (site A/site B has dedicated circuits) and so forth. As @Mohammed al Baqari mentioned you may be better off looking to hire a Cisco Unified Communications Engineer to assist with this rollout.
------------- L. K. | Consultant, Lead Senior Engineer, Specialist | Cisco Unified Communications