I'd say at least mid-high jounin level. I'd say he is about as strong as part one Kabuto, Asuma and Sai. He is probably higher but needs more feats to show what he is capable of.
He has Sasori's puppets now. I think that Instead of using Sasori's power he should just make his own insane puppets. Sasori's puppet could slice through rocks and clouds with just water.
Anyway, Kankuro might not have super haxx powers like the main characters, but he's still a very talented ninja (or else he wouldn't have been named a jounin or captain, now would he?)