which plant

How about Wisteria? I think that it meets your criteria, but it often takes time to flower. In the meantime, you could grow other climbers like Actinidia kolomikta or Solanum laxum 'Album'. There are of course lots of lovely scented climbing roses that you could team with a couple of Clematis flowering at different times to lengthen the season.

Clematis Almondii and a David Austin climbing rose together. The clematis has white flowers early on which have a gorgeous scent and the rose will flower in the summer. You could also add something for autumn/winter colour - Virginia creeper??