Hello Ridhwan
Yes it is possible to perform equal cost load balancing across branches in this way. However, because each path is in a different OSPF area, there are nuances that you should keep in mind. Based on OSPF good practice and design, any routes found in Area 10 should not be found in Area 20. Each area should advertise its own distinct networks. So load balancing cannot occur when trying to reach networks in either Area 10 or Area 20. However, load balancing can occur if you are trying to reach networks in Area 0 (to which both Areas 10 and 20 are connected) and beyond, such as additional OSPF areas and networks outside of the OSPF domain. So load balancing will only take place assuming that you are trying to reach networks outside of Areas 10 and 20.
Secondly, load balancing will only take place with OSPF if you have equal costs. When traversing different areas, the cost to reach a particular destination may be modified by the ABRs, so you must make sure that the cost is indeed equal.
So it’s possible, you just have to keep in mind some of these nuances to make it work.
This is inherent to OSPF and is not due to the use of multiple areas. If you want to speed up the OSPF convergence process, you can do so by using some features such as LFA FRR. You can take a look at this lesson for more information:
Alternatively, you may also consider using Bidirectional Forwarding Detection for faster reconvergence:
If you have one switch become the root bridge for all VLANs, then you will have one of the links completely idle as it will be blocked for all VLANs to avoid a Layer 2 loop. It’s a good idea to make one core switch root bridge for half of your VLANs, and the other core switch root bridge for the other half. That way, you have a more efficient use of the layer 2 links.
I hope this has been helpful!
Laz