The bridge priority is a customizable value that can be used to influence which switch becomes the root bridge. The switch with the lowest priority, which implies the lowest BID, becomes the root bridge because a lower priority value takes precedence.
The default priority value for all Cisco switches is the decimal value 32768. The range is 0 to
61440, in increments of 4096. Therefore, valid priority values are 0, 4096, 8192, 12288, 16384,
20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, and 61440. A bridge priority of 0 takes precedence over all other bridge priorities. All other values are rejected.

The tunnel destination will be known by the tunnel interface when we do traceroute.
Please note that ospf protocol on Site A and Site B routers causes error " %TUN-5- RECURDOWN" which keep on flapping the GRE tunnel. Only upon removing the ospf configuration the GRE tunnel will become normal.

In this case, we are using your EtherChannel without a negotiation protocol. As a result, if the opposite switch is not also configured for EtherChannel operation on the respective ports, there is a danger of a switching loop. The EtherChannel Misconfiguration Guard tries to prevent that loop from occuring by disabling all the ports bundled in the EtherChannel.

A prerequisite for configuring Mobility Groups is "All controllers must be configured with the same virtual interface IP address". If all the controllers within a mobility group are not using the same virtual interface, inter-controller roaming may appear to work, but the handoff does not complete, and the client loses connectivity for a period of time.
https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-5/config-
guide/b_cg85/mobility_groups.html

Authentication: As mentioned, the Cisco SD-WAN control plane contributes the underlying infrastructure for data plane security. In addition, authentication is enforced by two other mechanisms:
In the traditional key exchange model, the Cisco vSmart Controller sends IPsec encryption keys to each edge device
https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/security/vedge-20-x/security- book/security-overview.html