The only passie I have with small leaves is the P. murucuja. The blooms are surprisingly big for such a small delicate vine. The stems, including the main one are so thin on this variety. I'm not sure how thick the main one would get but it could be an interesting experiment. I'd say the largest leaves are only about 2" across, if that and they aren't lobed.
Karyn

I meant to say that the leaves aren't multi lobed. They are kind of fan shaped.
Karyn

I'm not at all certain you could bonsai any type of passiflora. The stems don't get woody until the plant is quite mature, and they only flower on new growth, so continually trimming them back would be counter-productive if you want flowers.