You can't do that with policy-based tunnels.
You have two choices:
Keep the policy-based tunnels and setup Dynamic DNS and gateway groups on both sides so that if a WAN fails, the switches the hostname and single IPsec tunnel to the other WAN. This works, but takes a long time to switch since it relies on DNS (several minutes, most likely)
Ditch the policy-based tunnels and use VTI. Configure two tunnels (1.1.1.1<->3.3.3.3, 2.2.2.2<->4.4.4.4) and use FRR with either OSPF or BGP to handle the routing. When setup properly, dynamic routing protocols are smart enough to detect when a path is down and use the other alternate path in a timely manner.