Definitely contact the pool contractor first. I think you need the landscaper to work around the design of the pool and not vice versa.

It's the reverse, landscape designer sites the pool and dictates its shape and size. LD is the generalist who fits everything together.

We design and build so we can come up with a landscape design or we work with a landscape architect on large, involved projects.

No matter who's called first, they must find out what your town/city will allow you to fit in your property based on setbacks. That's a starting point that will drive the pool size. Some towns have a code regarding maximum impervious coverages which also have an impact on pool size.

The idea is to get the PB and the LD to work together for a complimentary design.