It would be much better to grow the climber in the open soil than a pot, which has limited rooting space, or to cut a hole in the concrete, which is easier than it sounds. It might be possible to grow the stem of the climber along the ground first and then up the porch.
I want to grow a Clematis up & around my front door but my lawn is a few feet away from the door. Is it possible to grow Clematis Montana in a large container or do you have another idea for a hardy, fast growing, flowering climber?
Clematis montana is perhaps a bit vigorous for planting around a doorway. Some of the summer clematis, such as Clematis jackmanii, might be better.