I don't know much about KVS and I've never booked an award on CA (using UA miles) so my info may be of limited to use. However, I have booked many tickets on CZ using NW miles and can only assume that UA-->CA entails a similar process.

When you make a booking, NW sends a request to CZ and CZ then responds with a "yes" or "no". I've found that, by simply calling CZ, getting to "yes" is pretty easy. In fact, on several occasions, I've called CZ from NW's office during the booking process and walked away with tickets in hand.

Furthermore, I would venture to guess that CA is at least as accessible in this regard as CZ because its overall customer service is significantly better IME (i.e. CZ is a really bad airline, while CA is so-so.)