Have been to Kanchi a few times, the last visit being just a year ago. There are so many temples to visit (I have been to a few, dont remember all their names), the most famous being the Kamakshi temple and Ekambareshwar temple. You should also go to the ’Vulagalandha Perumal’ temple. This is where Lord Vishnu measures the world with his feet. In many of these places, you feel transported back in time and you feel more than a little sad at the maintenance.
You can also visit the Sankara Mutt, which is the seat of the Kanchi Sankaracharya.
And if you want to shop, check out the gorgeous silk saris. Even lovely cotton ones in bright, earthy colours. You also get dress materials.
The place itself is a bustling, crowded, dusty town. Still, if you are thereabouts, worth a visit. Two days should suffice. Summer would be blistering heat though.