There are many designs to implement high-availabilty A in DMVPN. Basically, design decisions depend on the infrastructure, budget, and on whether you are looking to implement HA for DMVPN devices, ISP links, or both.
on your scenario, you seem looking for implementing ISP redundancy for DMVPN HA at the spoke side. This scenario can be achieved by Dual-cloud Single-hub design, also with double-hub it can be more highly available.
The design elements for your scenario:
- two tunnel interfaces using two source physical interfaces in spoke.
- two tunnel interfaces in the hub, they can share the same physical interface.
- Key point: using dynamic routing protocols in the two clouds with different "link costs", so that the primary connection has the lower cost, and the secondary connection has the higher cost (to be used upon failure)
I Hope this helps you