BB-CE full config :

!
track 1 ip sla 10 reachability
!
track 2 ip sla 20 reachability
!
!
interface Ethernet0/0.1
 encapsulation dot1Q 100
 ip address 10.10.10.1 255.255.255.0
 ip nat inside
 ip policy route-map COLT_PBR
!
interface Ethernet0/0.2
 encapsulation dot1Q 200
 ip address 20.20.20.1 255.255.255.0
 ip nat inside
 ip policy route-map BT_PBR
!
interface Ethernet0/1
 description ISP_COLT
 ip address 172.16.10.2 255.255.255.0
 ip nat outside
!
interface Ethernet0/2
 description ISP_BT
 ip address 172.16.20.2 255.255.255.0
 ip nat outside
!
!
ip nat inside source route-map ISP_BT interface Ethernet0/2 overload
ip nat inside source route-map ISP_COLT interface Ethernet0/1 overload
!
ip route 0.0.0.0 0.0.0.0 172.16.20.1
ip route 0.0.0.0 0.0.0.0 172.16.10.1
!
ip sla 10
 icmp-echo 8.8.8.8 source-interface Ethernet0/1
 frequency 10
ip sla schedule 10 life forever start-time now
ip sla 20
 icmp-echo 8.8.8.8 source-interface Ethernet0/2
 frequency 10
ip sla schedule 20 life forever start-time now
access-list 110 permit ip 10.10.10.0 0.0.0.255 any
access-list 120 permit ip 20.20.20.0 0.0.0.255 any
!
route-map ISP_COLT permit 10
 match ip address 110
 match interface Ethernet0/1
!
route-map ISP_BT permit 10
 match ip address 120
 match interface Ethernet0/2
!         
route-map BT_PBR permit 10
 match ip address 120
 set interface Ethernet0/2
!
route-map COLT_PBR permit 10
 match ip address 110
 set interface Ethernet0/1
!
!
event manager applet COLT_DOWN
 event track 1 state down
 action 1.0 cli command "enable"
 action 2.0 cli command "conf t"
 action 2.1 cli command "interface Ethernet0/0.1"
 action 2.2 cli command "no ip policy route-map COLT_PBR"
 action 2.3 cli command "exit"
 action 3.0 cli command "no access-list 120"
 action 4.0 cli command "access-list 120 permit ip 10.10.10.0 0.0.0.255 any"
 action 5.0 cli command "access-list 120 permit ip 20.20.20.0 0.0.0.255 any"
 action 6.0 cli command "no ip route 0.0.0.0 0.0.0.0 172.16.10.1"
 action 7.0 cli command "no ip nat inside source route-map ISP_COLT interface Ethernet0/1 overload"
 action 8.0 cli command "exit"
 action 9.0 cli command "clear ip nat translation *"
 action 9.1 cli command "end"
event manager applet COLT_UP
 event track 1 state up
 action 1.0 cli command "enable"
 action 2.0 cli command "conf t"
 action 2.1 cli command "interface Ethernet0/0.1"
 action 2.2 cli command "ip policy route-map COLT_PBR"
 action 2.3 cli command "exit"
 action 3.0 cli command "no access-list 120"
 action 4.0 cli command "access-list 120 permit ip 20.20.20.0 0.0.0.255 any"
 action 5.0 cli command "ip route 0.0.0.0 0.0.0.0 172.16.10.1"
 action 6.0 cli command "ip nat inside source route-map ISP_COLT interface Ethernet0/1 overload"
 action 7.0 cli command "exit"
 action 8.0 cli command "clear ip nat translation *"
 action 9.0 cli command "end"
event manager applet BT_DOWN
 event track 2 state down
 action 1.0 cli command "enable"
 action 2.0 cli command "conf t"
 action 2.1 cli command "interface Ethernet0/0.2"
 action 2.2 cli command "no ip policy route-map BT_PBR"
 action 2.3 cli command "exit"
 action 3.0 cli command "no access-list 110"
 action 4.0 cli command "access-list 110 permit ip 10.10.10.0 0.0.0.255 any"
 action 5.0 cli command "access-list 110 permit ip 20.20.20.0 0.0.0.255 any"
 action 6.0 cli command "no ip route 0.0.0.0 0.0.0.0 172.16.20.1"
 action 7.0 cli command "no ip nat inside source route-map ISP_BT interface Ethernet0/2 overload"
 action 8.0 cli command "exit"
 action 9.0 cli command "clear ip nat translation *"
 action 9.1 cli command "end"
event manager applet BT_UP
 event track 2 state up
 action 1.0 cli command "enable"
 action 2.0 cli command "conf t"
 action 2.1 cli command "interface Ethernet0/0.2"
 action 2.2 cli command "ip policy route-map BT_PBR"
 action 2.3 cli command "exit"
 action 3.0 cli command "no access-list 110"
 action 4.0 cli command "access-list 110 permit ip 10.10.10.0 0.0.0.255 any"
 action 5.0 cli command "ip route 0.0.0.0 0.0.0.0 172.16.20.1"
 action 6.0 cli command "ip nat inside source route-map ISP_BT interface Ethernet0/2 overload"
 action 7.0 cli command "exit"
 action 8.0 cli command "clear ip nat translation *"
 action 9.0 cli command "end"
!
end