I am extremely jealous!!! I LOVE that look! I have been trying to recreate it by fabricating my own out of rebar because they are so hard to find pre-made.

I would choose the roses based on the material of the tree guards and how strong they are. Here in CA, roses grow so large that it is almost better not to even use climbers, but to use lanky, arching roses instead. Our climates are totally different so I don't have experience with which roses would do well in that application in your climate. Climbing roses might be the best for you. I have been on the look out for this look so I have creeped a lot on gardenweb for photos and can forward you some of my favs... Here's some of the ideas from others on gardenweb...

Don Juan:

http://forums2.gardenweb.com/discussions/1593866/how-easy-it-is-to-work-for-with-rebar?n=24

Joseph's Coat and Climbing Pinkie (Joseph's coat is a half, against a fence, so that gives you an idea of what splitting them into 10 could be like): http://forums2.gardenweb.com/discussions/1670004/jandp-arches-and-pillars

Climbing Pinkie (this is the same one by Jim as earlier, but now it's all grown in -- this is my personal favorite!!!):

http://forums.gardenweb.com/discussions/2188367/climbing-pinkie?n=22

Here's my rebar rose "tree." I'm winding Don Juan and Henri Martin around the base and the trunk (like a pillar) instead of inside like in the other links I posted above (like a standard). Mine isn't grown in yet, but I think it gives you a good idea of what it could look like. http://forums.gardenweb.com/discussions/4243730/umbrella-rose-tree-trellis-in-the-making

But for french rose tree guards, I would personally plan on having the rose grow inside (like a standard). Based on how large they are, you might be able to split them in half and put them near a wall to make them into 10... but I would be more inclined to use them whole as 5 because they are so beautiful from every direction when you use them that way. It really creates a WOW factor. I am so excited for you! I can't wait to find out which roses you choose and see your photos!

The rose garden at the Staten Island Botanical Garden has/had some roses in similar supports. They weren't climbers, just roses that grew fairly lanky canes. The roses were planted in the middle, then did some arching over. I've seen long caned Bourbons grown this way, and can imagine many HPs. Basically, you are looking for something that grows to about 7 ft, and isn't particularly shrubby.

Whether or not they can be used as half-rounds will probably depend on how sturdy they are in the ground. If you can push it over, it isn't going to stay upright with a rose inside it. My guess is that they will need some sort of anchoring. Pieces of rebar drive into the ground, then attached to the tree guard is a minimalist approach that works.

If you like the Austin roses, there is a list on the Austin USA web site that names about a half dozen large/climbing potential roses that should be hardy for your zone. They are under, "Roses for Climate Zones.". Whatever you try, winter survival of a rose grown on such an exposed garden feature in your zone is critical. You don't want to have a rose that routinely dies to the ground after winter. May I direct your attention to:

A Shropshire Lad

Brother Cadfael

Eglantyne

Gertrude Jekyll

Golden Celebration

Graham Thomas

I've not tried any of them myself, but have been studying them for a possible try in my garden. Hope I have helped.

P.S. Madame Isaac Periere could work very well with its somewhat open, long caned growth habit.

I finally took a picture of one of the guards. I am guessing that a rose will have to be six feet to cover it, and much taller if it is to be wound around it. I loved the idea of a standard rose look, but can't imagine at this height it would work. I do like the idea of thin, flexible canes with an arching habit. Should I be concerned that some bloom on old wood and some on new wood? It seems a pain to have to re-train every season.. I have looked up the suggestions, and thinking these would be most suitable.

Amadeus (unless the red is an orangey rather than blue tinted shade??)

William Baffin

Eden Climber (Pierre de Ronsard)

Generous Gardener

Blaze climber (again - is the red in the magenta/blue family?)

Louise Odier

Thanks so much for the great advice. Please keep it coming!

I haven't sprayed yet and would like not to have to. My main problems have been japanese beetles, which I pick off by hand, and voles. So you approve of William Baffin? Are you recommending Captain Samuel Holland? I like its look.

Blackspot is the biggest rose issue in the region by far. Sometimes you can sneak by for a year or two before it finds your garden, but it will, and once it does most of the roses recommended here will suffer from it.

I've never really warmed up to William Baffin. I don't like the color or the growth habit. I wouldn't plant it. I haven't planted it. However, a certain amount of that is personal taste.

Captain Samuel Holland is a great rose. The individual flowers aren't spectacular. I've described it as climbing Knock Out, and that sums up it strengths and weaknesses.

Having no luck finding any nurseries with Capt Holland.. but I ran across Alexander McKenzie, another Explorer rose that seems to have the same attributes. Thoughts?

We've never grown Alexander MacKenzie because it has a local reputation of being very blackspot prone. About 20 years ago, it was the only Explorer that tended to be available locally, and it turned several people of my acquaintance off Explorers.

The supply situation for hardy roses has gotten totally ridiculous lately. Eventually, Palatine will become big enough and other nurseries will show up to fill the void left by Pickering.

I have 3 William Baffin in the backyard, I picked up 2 for $3 each when I knew nothing about roses, and bought one from the rose club. they're huge! 10-12' x 10'. They put up a big spring show, and after that the repeat isn't great, but Palatine has one repeats very well. I won't plant William Baffin around the tree guard, it will eat the whole thing in 1-2 years. :-) What about Pretty in Pink Eden? It climbs and repeats well. https://www.edmundsroses.com/P/25579/Pretty+In+Pink+Eden+Climber+Rose

If you like Alexander MacKenzie, you might like Florentina. Palatine still has that one.......