You dont turn on vbportal2 integration when your running vb3.
If you want to install with vb3 integration on install it is all automatic. You install photopost and on last step of install after integrating with vb3 it asks you paths and urls to vbulletin and photopost and you simply turn on the 3 vb3 integration boxes.
thats all there is to it
If your vbportal is correctly installed with your vb3 you will see a vbportal sidebar in photopost its all automatic.