The key for us will probably be early wickets, i.e. Sri Lanka's top four. Like South Africa, Sri Lanka have a middle order that can collapse. Lets be honest here, Samaraweera and Silva are decent players, but they're no where near world class ODI standard, and they're the only weak links I can see in this Sri Lankan side.
Also they do only play four specialist bowlers, so we can't allow Dilshan to get through cheap overs, but at the same time we can't allow him to take wickets. Also if we can get into their middle to lower order, with four specialist bowlers it will keep us in their innings longer as if someones on fire they could potentially lose their last five wickets for not many.
Sri Lanka without Murali would be a real real bonus, but I assume he'll play even if he can't field, as he's given us all sorts of problems in the past.
If McCullum doesn't do anything here he has to go back down the order, as he's not doing what an opener should do and score reasonably consist runs at the top. Guptill will more than likely struggle against their spin. Ryder and Taylor are both going to be wildcards who on their day could win us the match. Styris hasn't done much this World Cup, but down at five it doesn't give him much opportunity, this match could be his for the taking though as he's known to preform well under pressure.
Like the South Africa match, the heart says New Zealand, but the head says South Africa.