I know that cause I'm working on strategy it's somehow objectivism; on the other hand because it's related to human resource management it's subjectivism. Based upon Morgan's model (1987), what do you think?
It depends more on the kind of methodology you are going to adopt to conduct this study. Both positivist or interpretivist philosophy can be there. On the one hand positivism emphasizes the quantifiable/ measurable aspects of the research constructs, while interpretive philosophy is in contrary.
Since your are using Schuler's (5-P) model for formulating HR strategy. It is in my opinion a kind of Deductive approach where you test the theory whereas in inductive you build theories. Further we use a mix of qualitative and quantitative or either methodology to reach results in both. No strict norms as such, however, it is advisable to back deductive researches with quantitative data.
I think it should fall in trap of FUNCTIONALIST, however, Saunders (2009) strongly recommend that it is not either- or situation while using epistemology,approach or paradigm but it can a mix of them. and the mix depend upon the objective you set for your study. I hope I am clear now.