You do not "tie" a LAN port to a WAN port in any way. You can set up Policy Based Routing. With PBR you configure two routing tables, one for LAN1, one for LAN2. The routing tables will be chosen by source subnet. When traffic destined for the internet hits LAN1 PBR will see the source "192.168.7.0/24" and choose routing table #1 which redirects to WAN1 / ISP1. Traffic from LAN2 (192.168.2.0/24) will use routing table #2 and goes via WAN2 / ISP2.
See this tutorial: PBR - source address based
*edit
removed references to eth interfaces as they seem mixed up in the first post...