Re: Flying to Hawaii
Done it many times from LHR and unquestionably the best is via YVR . US use 'pre clearnace formalities at YVR and these are not that busy late afternoon when you get there for the onward sector to HNL.
Using any of the US airports reqires planning along interconnection due to the need to suffer the degrading treatment s called Federal Clearance formalities. Same proces in YVR but no pressure and nicer staff
Arrival in Hawaii is late evening and its not too busy as a rule but HNK is apoor airport with iys archaic little goldf buggy interterminal trains
Returning from Hawaii will likely require a daytime layover whether you go via US or Canada (it is possible to do it witha shorter connection in US but it takes a relaly early morning start in Hawaii). So you have ten ours or so at YVR a great city in summer-even if you do it in winter like I have to do the on airport Hotel at YVR is very nice and cheap for a day room too
Also remember if youare flying to one of the other islands than Oahiu then additional time for the inter island flight is required altho I think United might go to Hilo direct from LAx
PB
PB