Durango,
(Speaking over the extremely rude people who used your thread to talk about other issues) If you've conquered all of Kazan's provinces but no annex option appears when you offer peace, there is probably a peace offer from Kazan to you outstanding. Look in the top right of your map screen. There's probably a small shield icon there. Click it and you'll see their offer. Decline and then make your own peace offer.
Regards,
Maturin