I love Kan - it's a "home from home" for me in SE Asia. I've always got there by bus from BKK; if I remember rightly there is an express bus and a more leisurely one that stops more frequently.

I can also second shanek's suggestion for the VN Guesthouse. I've stayed there twice, getting "stuck" there for quite a while the second time. They have AC rooms out on a "raft" floating on the river which were pretty special. Nothing quite like putting your feet up outside on the balcony as the sun sets on over the river and you watch everything go by. The only weird thing is being woken up by the wake of boats chugging by - your whole room rocks as it's floating on the river - disconcerting at first, especially waking up after a few Singhas!

Have a great trip and please come back and tell us about it when you return!