Background This company has two divisions, A and B. For a year, my peer in A worked on tech X for A and B and was trying to position himself as "cross-divisional lead of X".
B hired me to build and independent X function. Management in B wants X, but also wants to keep good relationships with division A. I want to keep doing my job on X as independently as possible.
My peer in A wants full access to my work. I pushed back, and now we are having a meeting with senior management to discuss "working together".
During this meeting I expect to be put under pressure, with comments like "you are being difficult" or "it's always been like that". I also expect the manager of my peer to try and twist any of my statements into something that will make me look like a fool. At that point, I might become defensive and look weak, making a case for my peer to supervise my work.
On the other hand, it would be relatively easy to demolish my peer, as A) he has less business experience than me, B) he is from another division, and we are TWO different divisions, C) division B is trying to become more independent and having his presence goes against it.
On paper it would be very easy to say "we are two divisions, A and B, but of course we are going to be collaborating on specific projects, and if you need my help in A I am happy to advise", using the legitimate organisational structure to push back.
I can defend myself like that, but I risk damaging diplomatic relationships. Indeed, I might be thrown under a bus if management in B thinks I am damaging relationships with A. The saving grace is that top management in division B, while wanting to keep a good relationship, also wants segment X to become independent in division B.
Question: How can I push back my rival's request for full access to my work (projects and customers) while maintaining good relationships with the other division, avoiding demolishing that person?
(Note: I do expect that rational arguments will be twisted by her manager, e.g. "we are two divisions" met with "yes, but we are one company, we should work as one team...")