I think you could stagger cut the stems now and they would bloom a little later than the higher ones, but I'm not experienced in this problem. Then next year pinch out the tips of some or all of the stems when they start growing to produce a bushier plant.

Do you have a tree or large shrub growing close enough that you could tie a string between it and the arbor and train the long stems to grow into the tree? When my vit etoille violet got too long stemmed for its trellis, I trained it into a small Leonard Messel Magnolia about 3 feet away.

Or maybe you could use twisties to train the long stems over the top of the arbor & down the other side.

Marie in ME

Allowing a clematis to reach the top of your trellis is not going to make the plant stop producing flowers on those longer branches. The branches will continue to grow and eventually their own weight will make them cascade back down and over the other vines. The petioles will grab onto anything that is nearby and start clinging on to that.

If you pruned the plant correctly, which it sounds like you did, the plant will flower on its stems where it should flower. One thing you can do after you prune your plant in the spring is to start pinching out the growing tips of the side shoots that begin to grow after they have two or three sets of leaves. This will encourage more side shoots to develop and you will end up with a fuller plant. This may also allow the plant to flower lower down on the vines than they would otherwise.

Would need to see a picture to determine if the side shoots you are talking about are buds of flowers or just axiallary side shoots that will develop more stems.

Since you live in Ontario and I do not know your growing conditions or length of the growing season, I would leave your plant alone this year to prevent cutting off flower buds that might be the only ones you get this growing season. Next year, do your initial pruing back to 2 or 3 leaf nodes from the soil line and then start pinching back the side shoots as described above and see if that solves your issue.

Great thanks for hte advice. I pinched one growing lead off to see what would happen, and I trained some of the tallest ones onto an apple tree...the other ones seem to be making their way by themselves across the arbor to the other side which is good. I'll snap soeme pictures and post em later. Thanks agian!