Routing a proxy server connection to match the clients routing mark
I have a network that serves internet to 60 clients, all go through a mikrotik rb which routes traffic according to MARK_ROUTING rule in mangle.
So, Group1 goes thru WAN1, and Group2 goes thru WAN2 etc.

Now i want to setup a squid proxy to optimize browsing, but if i mark routing of the squid ip to Group1, then ALL the traffic will go to Group1 only.
Now do i have to have a squid server for each WAN connection?
Or is there a way to have all the clients go via the proxy, and the proxy chooses the WAN connection that matches the clients routing mark?

You can redirect that traffic based on routing/ packet marks.