That is a great web site...no, we didn't get a chance to choose our seats. It was done through the cruise line. I remember calling and being told they would give us our seat assignments when we checked in.
On the way home, we actually forfefited our seats through Radisson...purchased NEW seats and upgraded with miles. As it turned out, it wasn't outrageously expensive...it was something like $300 pp (NZ-LAX) for the coach seats, and that was at the last moment. The only problem was that we had to use RT miles for a one way ticket! That smarted a bit. It was WELL worth it. We all ate a good meal, slept until breakfast and awoke feeling great!