Do publishers typically prefer a more realistic approach to illustrating, or do they prefer the more cartoon like approach? In the one middle grade novella I'm actively working on, it's someone in between.
I'm wanting a minimalist realistic, rather than a cartoon style (to draw myself that is) where it's a "realistic" drawing, but you still see the outlines as if it were a sketch.
Each publisher and each book has their own needs. When deciding on which publisher to submit to, check their recently published books to see which styles they are currently pushing.
Make the best art you can possibly create. Choose a publisher based on your style, rather than choosing a style based on a publisher.