As @BrandonS stated, this won't work with the VPN solution you proposed, but there may be other ways of getting it to work - but you'd need to try them out.
Out of curiosity, if you're planning the same SSID at each location why the need for three internet connections? How are you planning to direct each stores traffic to the correct internet connection? And I'm not entirely sure how the Meraki Air Marshal will respond to 'seeing' the same SSID from a different Meraki Network (I'm sure that Air Marshal work on a per network basis, but happy to be corrected otherwise), which means you may also need some fine tuning of Air Marshal.
Maybe you can use a shared network with three SSIDs, one for each store, each with its own VLAN/subnet. You can then use the Bonjour Forwarding between them on the MRs or even on a MX in the shared network. For the internet connection, to keep them separate, you could use static default Source Routes on that shared MX to send the traffic from each SSID/subnet to a specific MX for internet access. The shared MX would also need internet connectivity through one or two of the other MXs too, but this shouldn't be to hard to achieve. This is just a thought in progress, so it needs some testing, and I'm sure others in here might have some input too to round out the solution (or to highlight the flaw in it).
