Morning @Surya10101, your design/thinking is correct. Your site to site connectivity is done via your FortiGates and your MRs/Wireless will be managed by the Meraki dashboard. Wireless traffic from one site will be able to traverse your WAN and reach the devices across your network. Just as long as your routing is correct and firewalls permit the traffic.
Darren OConnor | doconnor@resalire.co.uk
https://www.linkedin.com/in/darrenoconnor/
I'm not an employee of Cisco/Meraki. My posts are based on Meraki best practice and what has worked for me in the field.