If you are looking for a single clematis vine to climb a 9' trellis and then cover 20'of pergola, that's going to be a tough call. I can think of a couple of species clems that could potentially fit the bill but both are later flowering, hard prune types so you will be starting over again every season. And with not particularly showy flowers.

You could possibly do multiple containers that in combination may grow tall and spread enough to cover the pergola. But again, most of the larger growing and showy vines will be in the hard prune grouping and with the vines being so conspicuous, you will definitely want to prune to keep things clean and tidy.

It is also important to remember that container grown vines are unlikely to get as big as the same vine would if planted in the ground. I'd knock 20-30% off the estimated size of a mature, established vine if you are growing in containers. Even big containers :-)

Thanks so much for your comments. Would certainly love any recommendations. Currently I am considering, "Clematis montana Rubens" but would love more ideas

The montanas are not as cold hardy as many other types of clematis, typically rated only to zone 6b. And top growth can be knocked back during a hard winter or late spring freezes. Since they flower on old growth, flowering may be limited under those conditions.

Thanks for the input, do you have any suggestions for another type of clematis, or a different twining vine with vigorous growth that can exceed 20' in height?