I just had a look at the "facebook fan" rankings on Pundit's Guide:
Nathan Cullen (who seems to be last on many NDPers list) has the most fans at 5,105.
Peggy Nash is second with 4,329. Dewar third with 3,135. Chisholm fourth with 2,040.
Fifth, Brian Topp with 1,936. Sixth, Thomas Mulclair with 1,785. Seventh, Romeo Saganash with 1,545.
Eight, Martin Singh with 482. And surprisingly last, Niki Ashton with 382.
I doubt the balloting will look anything like this. I expect Cullen, Dewar, and Nash had higher levels of support online because they have been MPs longer (though you would expect Mulclair and Ashton to have a higher levels of online support as well).