My 18V 10 watt solar panel
Since we don't really know how much power the router needs on average, it is hard to size the panels. The 2A rating is most likely the maximum that is required, not the average. So my suggestion is to use two of the 20W panels in parallel.

You will also need some type of voltage regulator to protect the router from over-voltage.

Please note that the router will only function when bright sun is shining on the panels. If there are clouds, or shade from trees, or if the sun is low in the sky, the router will not function.

Also, under some conditions when there is not enough sun, the router may reboot over and over. Not sure if this could damage the router or cause other problems. This is kind of a complex problem to solve so I am not going to get into it. Just be aware that this might happen.