AC is pretty strict about missed flights on separate tickets -- often you have to buy a new ticket and the old ticket becomes worthless. They definitely want you to pay the higher price for single tickets instead of buying 2 separate ones and use this to punish those who do. No problem if you buy your own travel insurance which covers the cost of missed connections but considerable risk otherwise. Canadian immigration can often take over an hour to clear at YVR as they get overwhelmed when several 744s arrive concurrently (hopefully not the case for your scheduled arrival). Sometimes it is impossible to make a 2 hour connection. Also on a separate ticket you may have to check in with AC at YVR (NZ may not be able to do it for you in AKL), in which case AC check-in closes 45 min before flight time -- giving you 30 min to get off the plane, clear immigration, pick up luggage and clear customs, etc. Very tight, even with no delays!