Your neutral bar should be installed on some type of insulator; if it needs to be bonded you can use a bonding strap or a screw to bond it to the can. Your grounding bar may be mounted directly to the can or on insulators with a bonding strap or screw.
As far as your grounding, The NEC allows 2 scenarios:
1: You pull an equipment grounding conductor from the main panel with the supply (this is best IMO). In this case your neutral and ground are not to be bonded.
2: You pull no grounding conductor with the supply, you use a grounding electrode to supply your E.G. In this case you WOULD bond the neutral and ground at the sub panel.
