Walnut and maple wood do go together in many wood working applications.
Due to the strong contrast between maple's light color and walnut's dark hues, they create visual interest.
The combination of walnut and maple is a popular combination of wood in furniture making.
In woodworking and furniture building, the pairing of light maple with dark walnut creates a very stunning and high contrast look that is very popular in furniture design.
And figured or curly maple works particularly well as an accent wood with walnut.
And when finishing, some recommend that you avoid polyurethane for a more traditional look and instead opt for an oil or oil/varnish finish.
Although you should be careful when sanding and keep the sanding dust from contaminating each type of wood.