It is tricky.  On the one hand, local people should be selected.  On the other hand, a well-organized local politician can be a complete bozo and still get the nomination because of a small core of fanatics at the local level.  That is how our riding got stuck with Rob Anders for years and years, in a safe conservative riding.  If anything, there should be some allowance for parties to bring in qualified outsiders, above and beyond having them sit as MPs.  In the US, you don't have to be an elected politician to serve in cabinet.