The art chosen for trade publications is based on the editor's and publisher's preferences after viewing established illustrators' portfolios. So they already know what style to expect from the illustrator before hiring them. Depending on the publisher, there may be a lot of art direction or almost none. Generally speaking the author will be informed who the illustrator is and possibly sent samples of art in progress.
My experience with self-publishers has been them choosing based on price and speed and not style. Also, in these cases, the person wanted a family member or pet as the main character and micro-managed each and every element of the images. This made my job incredibly difficult and in the end, for me, neither conducive to my best work nor a quality product. There are self-publishers out there who understand the role of an artist to bring their vision to fruition, but it hasn't been my pleasure to be contacted by one.
My suggestion is to do your best possible work. If you are an artist, a trade publisher will pick based your style and needs of the project. If you are a writer going the traditional route, trust the publisher to pick the best possible illustrator to team with your manuscript. Each project is different, each book is different and so are the visions of the people producing the book for publication.
In the mean time find other illustrators with stylistic similarities to your art and see what books they've done.