I have today in my Mikrotik the following scenario:
LAN + 2 WAN / 29
On the WAN I include 2 addresses from each ISP in their respective interface.
In mangle I have created connection marks to direct the traffic that comes through an interface to return by the same and also a basic failover on the routes with ping check in the gateway.
I need to direct an IP of the LAN Subnet to exit by specific IP of the WAN and I am having difficulty doing this. I saw many posts indicating use src-nat and to-adress = "WAN SPECIFIC IP" but it did not work.