LTE failover setup over VLAN to device without USB port

Pretty much this
I trying to upgrade my setup and I'm stuck with a router without a USB port as most powerful one in the setup. If I could use the other device with USB port or Pi to dial and maintain wwan0 and provide a gateway to "main" router over VLAN.

It is possible, but the design is not correct. The device with the LTE will be connected downstream to the main router only. Then the main router will have the main internet connection and the uplink to the LTE router as backup in mwan3.

@trendy could you pls elaborate a bit on this?

I am also trying to setup scenario, where i use one device with 2x wlan 1gbit for failover (was thinking about ubiquity edgerouter (not sure if it can do really 1gbit) , but i want to also use GSM/LTE mode as a service connection in case both wlan are dead (as my both providers are crapy...)

thanks

not really

Use a USB LTE stick for that.
Prioritize the connections in mwan3 accordingly to use the wlans first then switch to lte.