Virajpet - Iritty - Mattannur stretch is horrid. Especially during monsoon (At least during 2006 July till November), the roads simply did not exist. First hand experience.
Vehicles not concerned with permit restrictions (that is, all vehicles except route buses) took the Mananthavady route to go to Mysore from Kannur.
See this link -
Kannur travel guide - Wikitravel
Mysore - Mangalore - Kasargod is a very long road, but excellent condition.