Not particularly familiar with either the NZ or Canadian system, but mixing and matching between the 2 aviation regulations could be a problem. It certainly would be if you were trying to do the same thing involving the UK. The CAA would make you jump through all the UK/JAR hoops almost as though you had no previous flying experience or licences from elsewhere.
However, there are cases where training in one location is specifically set up form the start to conform to the requirements of two national requirements. I believe that there may be some places in the USA where you can do both a FAA and UK/JAR licence, for example.
The idea about working both summers seems to be sensible, in princple, but wherever you work you will certainly need to have the national licence (obviously). The final answer will presumably lie with the national aviation authorities concerned. I would suggest that whatever you plan to do, you get a clear statement (preferanbly in writing) from them about how you might go about satisfying both sets of regulations.