Connecting two Sites over L2 Ubiquiti Antennas

[l4zz4r0]

Hi there,
I need some help to create a failover configuration between two remote company sites actually connected with radio link (ubiquiti L2).

• Actual scenario :

SITE A -> L2 Ubiquiti Antenna -><- L2 Ubiquiti Antenna <- SITE B
SITE A NETWORK (192.168.0.0/24) SITE B NETWORK (192.168.0.0/24)
Both sites rely on the same network range.
all works fine

Now I would like to install a second backup antenna and this would be the configuration I would like :

SITE A -> pfsense box -> MAIN L2 Ubiquiti Antenna -><- MAIN L2 Ubiquiti Antenna <- pfsense box <- SITE B
SITE A -> pfsense box -> BACKUP L2 Ubiquiti Antenna -><- BACKUP L2 Ubiquiti Antenna <- pfsense box <- SITE B

I know I need two pfsense box, one for each site.

But I don't know how to configure them exactly...they must make the network transparent to each SITE and provide failover mechanism.
Maybe a bridge ? and then configure failover ? The hard part for my knowledge is not the failover mechanism (I already configured other pfsense box for this kind of purpose) but how configure pfsense boxes to bridge two sites and make same network transparent for both as actual scenario do.

Please help

Regards