Branch Router ---MPLS and Internet using sub interfaces for VRF connection but we have a single physical link with two VRF terminated to our CE router.
Q1. Can the exisiting set up be used for setting up Meraki SD-WAN?
Q2. Is new public IP is required to set up the SD-WAN? Q2. Can we use MPLS or Internet VRF for site to site connection between branches using Mx100/Mx64? Q3. Can we use only MPLS VRF for site to site connection between branches using Mx100/Mx64?
There are some complications, because you are presenting the Internet and MPLS circuits on the same port using VLAN tags. You'll need to break these into seperate ports.
Lets pretend your provider is using the tag 2000 for the Internet circuit and 2001 for the MPLS circuit. You would need to plug this info an MX LAN port configured as a trunk port. You would then configure another port as an access port in VLAN 2000 and run a cable from that to the "Internet1" port on the MX.
How you treat the MPLS circuit depends on weather you want to run AutoVPN over it, as in this case:
This is the most difficult to deploy case, but the most sophisticated and provides the most SD-WAN configuration options. If you used this case you would run a second cable in VLAN2001 to "Internet2" on the MX.
The second way is to treat the MPLS as a simple routed circuit and only use the Internet circuit for failover, as in this case: