Hello Anthony,
from your diagram seeing IP addresses belonging to same IP subnet on SP2 network, it looks like SP1 is providing you an MPLS L3 VPN service and SP2 a sort of VPLS service.
In this case HQ router(s) and Branch routers will have an eBGP session with SP1 PE nodes and an iBGP or eBGP session on SP2 point to multipoint.
if you use the same AS number on all of your routers eBGP routes are preferred over iBGP routes (coming on SP2) and you should be fine.
to be sure of this you can use
neighbor SP1-pe-address weight 40000
on eBGP session with SP1 PE node if SP1 is providing you an MPLS L3 VPN service
to handle the double link between HQ and SP1 you can peer on loopback address using
int loop1
desc for eBGP over parallel links
ip address A.B.C.D 255.255.255.255
no shut
ip route SP1-pe-address 255.255.255.255 pe-next-hop-link1-address
ip route SP1-pe-address 255.255.255.255 pe-next-hop-link2-address
router bgp YourASN
neigh SP1-pe-address remote-as SP1-ASN
neighbor SP1-pe-address ebgp-multihop 2
neighbor SP1-pe-address update-source loop1
neighbor SP1-pe-address weight 40000
neighbor BR1-ip-address remote-as YourASN
....
! network commands to announce HQ subnets
network 10.10.10.0 mask 255.255.255.0
SP1 needs similar configuration with static routes to A.B.C.D and the other commands
without ebgp-multihop 2 the session does not become established, an active state is not a good sign in BGP.
A similar setup on branch side with network command used to advertise remote site subnets only.
For added security you could think of using route filters to ensure to do not advertise unwanted prefixes.
Hope to help
Giuseppe
