Hi Stanly,
Just a big picture regarding the Cisco SD-WAN.
1 Meraki is like a cloud base which the meraki router automatically get configured via cloud and you can have a web login to control, manage and access devices.
2. iWAN is a CLI configuration for ISR (G2) and ASR using DMVPN, EIGRP, and PfRv3.
3. Viptela is a hardware base which you have a Server that can control and manage viptela edge router. Currently still in progress with Cisco and possible integrated to ISR and ASR IOS-XE to become a edge router.