I'm not in your zone, so I hesitate to offer suggestions, but I often check out websites that sell clematis plants to see what they say about hardiness ratings. Some that I like are Silver Star Vinery, Brushwood Nursery, and Hummingbird Farm, which is in Maine. I've never had a clematis that went wild and spread all over, although some do get big, like Huldine and Sweet Autumn. Really, I think I would just start looking at web sites until you find something that appeals to you, and then come back and see if people have feedback about a specific plant. The looking is the fun part.

In your zone I wouldn't plant any clematis in the trunk since you want them down in the soil to stay warmer in winter. They like even moisture, which would be more difficult to achieve with them up in the trunk planter. Also, clematis are one of the unusual plants that prefers to have its growth center planted several inches below soil level, so that will help it survive your zone 3b winters, especially if mulched.

To get a list of zone 3 hardy clematis, use the Clematis on the Web search page (though not all the clematis have listed hardiness info), or if you consistantly have good snow cover by the time it gets really cold, you could plant a zone 4 clematis. Once you have a list of what types will survive your zone (mostly alpina, macropetala, viticella, and some integrifolia varieties) you can visit the websites listed by Opheliathorn to see who has some of them listed. (All have really nice clematis.)

Here is a link that might be useful: Clematis on the Web search page

If you have nurseries close by visit them and see what they are selling for your area. A nonclinging or lax clinger rambling vine would work great. Not sure of hardiness but check out Recta, Roguchi, Inspiration. Recta is listed as fragrant but check the plant in bloom before you buy as mine is not or it is so subtle that I cannot detect the fragrance. Also shorter varieties of vining clematis would be lovely.

I believe that hardiness ratings for clematis are not well established but am including a link to clematis.com which has hardiness rating for various varieties listed.

Here is a link that might be useful: Clematis listed with hardiness ratings

Thank you mnwsgal, I will check out those varieties. I have plenty of time to think on it. I still need to get the bed around the trunk in condition to plant. The way things are going, I might not be planting until next spring! Although I have been thinking about trying to propagate some of the clematis I already have, and trying one of those.
I have:
Jackmani
Henryi (alba)
Dawn
Nelly moser
Villa de Lyon
and a red one I can't remember the name of off hand

Here is link to suggestions for clematis on the Far North forum.
I see many are Z:3 posters.

Good luck on propagating your clematis. Those are all nice varieties.

Dang rain! Either too little or too much. I have two new beds that I'm trying to finish adding compost to so I can move plants from holding bed. These are large beds with lots of wheelbarrow loads of compost to move. Most of the plants are in pots so may have to dig up pots and set them on the patio so I can plant my extra tomatoes in the holding bed. Light rain today but supposed to be dry here tomorrow and Monday so maybe by late Monday I can get the extra tomatoes, peppers, beans and cucks planted. Then more rain expected the rest of the week.

Here is a link that might be useful: Your Best Clematis

Thanks for the link.
Yeah I agree about the rain, and it's supposed to be cool (60's) and wet up here for the next 10 days. Which stinks, can't get any work done outside, and I leave for 2 weeks on the 10th for a business trip. sigh
At least the drought is over!