Actually transit at LAX is marginally easier in the LHR-LAX-AKL direction (ie on NZ1), because typically immigration is not as busy. On NZ2 I expect it will take up to an hour (and can be longer on bad days) whereas on NZ1 I expect it will take 30 minutes. Security queues are a bit hit and miss at the time of transfer in both directions (ie can easily take 30 minutes). Of course on US passport immigration times are less, but the other (non-Canada) international arrivals at T2 around the same time will still be relevant.