Multi WAN for multi LAN routing and configuration

Hello,

I'm studying a project of multiple ISP and multiple vLANs.

Each LAN have access to specific WAN connection.

Here is the project :

- I have 6 differents LANs (LAN1, LAN2, LAN3 and LAN4).

- I have 3 different WAN connections (WAN1, WAN2 and WAN3).

I want to route specific LANs to specific WAN connection.

For example :

- LAN1 has access to internet trough WAN1 and (WAN2 and WAN3) are backups.

- LAN2 has access to internet trough WAN3 only.

- LAN3 has access to internet trough WAN2 and WAN1 is backup.

- LAN4 has access to internet trough WAN2 only.

I've looked on SD-WAN functionality, but in my case I have to had multiple SD-WAN (SD-WAN1, SD-WAN2, etc...), and it doesn't look like to be possible.

PBR can solve a part of thoses problems but I'm loosing the failover features.

I know it's very easy to configure with other brands and I'm very surprised that is not as simple on Fortigate.

I'm sure I'm missing something...

Is somebody can help me ?

Thanks !