You use a generic term 'router' in your question. But I am going to assume by router you are talking about a typical router design for consumers which will basically include one interface that connects to the upstream network, and the internal side of the router is presented on a 3-6 port switch/hub.
You should treat consumer routers as if they are two/three devices Switch + router + wireless access point. So assuming you are talking about a consumer router, you should ignore the fact that it has a router feature, and possibly wireless AP feature. From the perspective of the switches it is simply another switch, and you have 3 switches in a triangle.
If these 3 switches do not support spanning tree, then you will kill your network because you have created a switch loop.
If your devices do support spanning then one of the links will be disabled to prevent a loop. If the algorithm is operating properly, then the slower 100MB link will be deactivated instead of the two 1GB links.
So a full mesh setup (each switch is connected to other two) gives you some redundancy, but it does not give you additional bandwidth.
If you needed additional switch to switch bandwidth, then you would typically would do that with bonding. This allows you to combine the bandwidth of multiple links (with certain restrictions). Bonding requires a more advanced switch then you will typically see as consumer equipment though.