How to install GNU/Linux on ADSL router to setup internet watchdog?

What model of ADSL modem/router by major market brand can be used to install some distro of Linux to setup a watchdog to initialize connection by demand in case for example of main internet connection fail? Probably using C#/mono.

From serverfault abatishchev

• How about something like a Draytek 2820 or 2930 that supports 2 WAN connections with failover or can failover automatically to a 3G connection?

  If you do want a DIY solution, have a look at this wiki page over at dd-wrt

  abatishchev : Thanks! What is the different between dd-WRT and OpenWRT?

  abatishchev : btw, my main channel is high-speed ethernet and a reserve one - low-speed adsl
  From Linker3000