You don't really prune climbers. You want the canes to go as much sideways as you can get them. If you let them grow straight up, they will only bloom at the top. Get them at an angle, and you will get breaks all along the canes, that you deadhead for repeat blooms. (if it's a repeating climber) You want to be gentle, and not force the canes to bend. Don't crack them. It might take some time. This guys videos helped me with everything rose related. Here is one on climbers. https://www.youtube.com/watch?v=Rf7F5qhChFM

Here's mine, out of control, left to be himself. A manzanita volunteered there too.

OK, I will wait til winter to wind canes around the tree guard. Can you tell me WHY one should not prune climbing roses? If the canes at the best are simply too many or too widespread for the space, does it hurt the rose to thin them?

Bite the bullet and plan on moving it to somewhere it can be itself. It is going to be a constant struggle to get this rose to be what you want it to be in this space.

Any time you prune a rose you are removing food and flower making leaves. Also, climbers can throw hissy fits if hard pruned, and hardy climbers are notoriously difficult to train. The genetics aren't there for flexible, trainable canes. The best you are going to be able to do is a neater version of this.

While it is true that some roses sulk and do not like being pruned, many have no issues whatsoever with it. The bigger and more canes a climber has the more energy it can make to bloom. Now if you look at many of the gardens in public places you can quickly realize there is no way those climbers are kept neat and perfect without some sort pruning. I personally follow the head gardener of Cotswold Garden which goes by the name of niff_barnes in Instagram and she is also being followed by Michael the main David Austin rosarian. She does yearly training and pruning of unnecessary canes in all of their climbers (they have many). The key is to NOT prune the main canes, but many of the laterals can be pruned to give you the desired look. Looking through some climbing rose training videos and Instagram pictures could help you get familiar with it.

Sheila your Florentina is the most beautiful I ave ever seen, is it growing without a trellis and self supported? I don't favor a lot of reds, but this one is just too stunning.

Sheila, those pics of Florentina really capture her colouring. Just beautiful. To the OP, yes keep the main canes and try to pull them horizontal and prune the laterals after blooming. I personally wouldn't prune for the first three years on a climber. I'm inclined to agree with Mad about moving this one so it's not directly in front of that window and like the idea of growing it up onto the roof. P.S. Where do you live?

Dianela, Mad and Vapor thank you. Florentina here is left alone no support and looks really happy. I really agree with Mad that this is not the rose for a spot you want a mannerly plant you want to direct and control. Why put yourself through that, when other roses would naturally fit the space and needs better?