Can I shape a climbing rose into a nice round bush?
You can with some of them. Others just will not stay in the roundish shape and will send new growth out beyond the bounds you would like frequently. I have done it with a climber called Altissimo, beautiful big red blooms. It is a matter of wills sometimes I must admit! If you keep after it and keep the bush trimmed back, it may hold fairly well. With some climbers this will also cause a lack of blooms. With some of the older climbers you may well lose all the blooms as they bloom on the "old wood" or the last years growth. So pruning them back a lot will sacrifice blooms.