Figure 3 in there represents what I would like to achieve.
However the MPLS provider does not offer multicast support. In addition I read I need to increase the MTU and I'm not sure that will be possible across the MPLS cloud. So my question is what solutions might be applicable here? Can I run multicast over a tunnel across the MPLS core? Can I disregard MTU issues and let the devices fragment ?
If you have that exact topology (1 or 2 Leafs per site), you can get rid of Multicast and use only static ingress replication, setting peer IP 100.100.100.2 in Leaves 1 and 2 NVE, and peer IP 100.100.100.1 in Leaf 3 NVE. Multicast brings enhancement when you need to handle one-to-many Leaves traffic, where ingress replication is possible but suboptimal.
Regarding the MTU, there's no magic. If your provider stucks to 1500, you will need to set MTUs to 1450 on your infrastructure.
Static ingress replication looks easy and perfect for my requirements. I will have a vPC pair at each site so I assume I use a different loopback for the NVE on each vPC member and define both those as a static mapping at the other site. So each vPC member will have 2 x static ingress mappings. One for each vPC member at the other site. Apart from that the rest looks pretty straight forward and no multicast makes sense since I only have minimal VxLAN devices at 2 sites. I don't think I need the secondary loopbacks as shown in the diagram above. Is that correct?
Exact, except you will precisely configure the secondary IP on the single Loopback. On both VPC members, that second IP will be identical (like 100.100.100.1 on the diagram example) and will represent the pair. It will be a different IP for each VPC pair obviously. You can just follow this configuration guideline: