Rose trees aren't hardy in zone 5 because of the graft. You can try one in a pot and bring it in to an unheated, attached garage for the winter. It should survive if your plant stays dormant and the garage stays just slightly above freezing. There is exactly one rose tree that is hardy to zone 5 called Polar Joy. It isn't grafted which is why it is hardy. It is a very large, hardy rose that is pruned like a tree.

If you like April in Paris, I can let you know in the spring if the plant is hardy. I don't do rose trees, but I bought the regular version last year and it does have pretty blooms.

7b and higher, in my opinion. They aren't reliably hardy here in near-coastal central NJ.

There should be a law against selling tree roses in zone 6 and colder. Unless great care is taken they end up being expensive annuals.
The grafts are the weak points especially the top one. A rose rated to zone 3 is still grafted onto a root stock that might be rated only to zone 6. The graft is comprised of two slightly disimilar tissues. If there is not a really tight bond between these, a thin film of moisture can occur which will freeze in the winter. The freezing process can cause the tissues to separate and destroy the graft bond, killing the top grafted variety.

After many years of trying with various tree roses, I gave up until Polar Joy came out. Even then I lost the first one because it was planted too late in the ground, outdoors. The replacement was planted in a really big tree pot and is transported into my unheated greenhouse each fall. I've had it for 4 years now and it seems to be thriving.
By early April when it's moved outside, it's leafed out and beginning to set buds. It's my first rose to bloom, blooming by late April.
My advice, Rob, would be to not buy a tree rose in your area unless you are prepared to grow it in a large pot and have a place to move it into during the winter. If you must have one, start out with a miniature or patio tree rose. They're shorter and easier to haul around. They don't require as big a pot as a full sized one.
April in Paris is rated 6b and higher as a bush, 6b being the warmer half of zone 6. As a hybrid tea and grafted onto a standard (tree) it would not survive outdoors without a lot of difficult to apply, winter protection.
You'll notice I'm in zone 5a same as you. We have a very similar growing climate so you can expect similar results.
In my third year of growing roses, I had to have it all. I ordered 4 tree roses from J&P. They lasted three years and I buryed them each year to overwinter them. That was over 20 years ago and they were less expensive than now. I've learned a lot since. Not growing tree roses in zone 5 is one.

Thanks everyone for the info, although very discouraging.

Karl - I'll check out the polar joy or a patio tree rose, but my garage is not attached, and while about 10 degrees above ambient temp. in the winter, can still get pretty cold.

Athena - I really do like the april in paris HT as well. If it can make it through your winter, it should make it through ours. Let me know how it does in the spring.

This is one of the reasons why I loathe Home Depot and Lowes, they always get a order of dozens of NON hardy roses on NON hardy grafts every year as tree forms.. I talked with a manager at lowes one day about this. He gave me a whole bunch of curt/pat answers IE they get the same stuff that all of northern new england range etc...

I told him its a shame that you are really discourging people to try roses,

Lets not get started on what I told him about the darn knockout and flowercarpet roses they always push. Niether which are hardy in my area. Yet they seem to be EVERYwhere in all the nurseries.. I can only figure this will eventually stop when people stop buying them. But who knows.

Silverkelt

rob, My unheated greenhouse is not attached either and the temperature inside can get down to near that of the out doors. All my potted plants survive. I thinks it's mainly due to the fact they aren't exposed to the drying winds and harsh extremes of being outside or the freeze thaw from outdoor temperature swings.
Polar Joy is suppose to be hardy to minus 40 as a tree rose, but is quite expensive.
The miniature and patio trees are somewhat less expensive, so their loss won't be as hard on the pocket book.
Being in an unattached shed or garage would work. You want the bushes to get cold and even freeze. Some place a quilt or heavy blanket over them after the soil in the pots freeze. There are many experienced rose growers in Michigan and I'm sure some grow tree roses.
Try the link below to locate a society near you. You may find someone who can share their experience.

Here is a link that might be useful: state by state list of local rose societies

I have been growing an Austin tree rose for 3+ years that comes into my attached garage for the winter in a dark place. It does fine, but keep in mind the lowest temp in the garage all winter is still slightly above freezing. I would be afraid to try it in an unattached garage or shed unless you've gotten a good deal on it and won't be out much money.

I will say it is a hassle pulling the thing in every late fall as the pot is very heavy. And then dragging it in and out in the spring to get it acclimated again. It is a lightweight faux terra cotta but it has to be large enough for the rose roots to grow. So even when the soil is dry it is heavy to move, plus top heavy. We have it on a wheeled cart along with some other potted plants I bring inside and this makes it easier to haul in and out as long as I can stay on pavement. I have to be vigilant in pruning it after each flush, otherwise it gets top heavy and has actually fallen down in the wind a few times. I go through this trouble because it's a beautiful and fragrant rose.

The other tree rose I care for is Polar Joy at my client's. It is 100% hardy, sometimes I think it's William Baffin except for the rebloom. Hardiness aside, I also have to keep this one pruned often to keep its tree shape, otherwise long canes will grow sticking out all over the place. And I'm constantly having to keep up with the suckers. No I don't have to drag it inside in the winter, but the tradeoff is that it's just a single petaled, generic pink rose with no fragrance at all.

Silverkelt
Stores stock and sell what people buy. We, as a group, do not represent the rose buying public. We buy a miniscule amount of roses compared to the general rose buying public. They buy what's popular and/or easy to grow. They also buy the flower, not the variety. We look for specific varieties and most often will pick up a rosebush at a big box store only on an impulse.
Tree roses, in bloom, are attractive and therefore sell. All the hype about Knock Outs and Flower Carpet roses have caused people to look for them.
The big growers supplying these big box stores have to decide what will sell 6 months or a year before they appear in the stores. Tree roses, Knock Outs and Carpet roses are what sells to M/M average rose buyer. Don't blame the big box stores.
Even the garden centers and nurseries are catering more and more to the general public.
That's what keeps the mail order suppliers in business.
My hope is that a Knock Out or Flower Carpet purchase will be the start of a life time love of roses. If a new rose grower has good luck with a Knock Out they may soon look for other varieties. I sell hardy own root roses that I know will grow in my area with minimal care. Successful buyers have returned looking for more rose to add to their gardens. That's how we get them hooked!

I do agree though that buying a tree rose in a cold growing zone can cause an inexperienced potential rose grower to give up growing roses.

I have grown 2 Polar Joys as standards and 1 as a shrub for 6 or 7 years. I agree with Veilchen about it. It is perfectly hardy, but really wants to be a shrub. It sends up new canes. The canes it has as a standard want to be longer than I would like, but, and it's a big but, it's a fabulous shrub.

Steve.