For best results, use 125-300 dpi at size.
Note that some matte papers and Canvas Wraps are more forgiving since the texture tends to hide some of the detail. Also, keep in mind that the number of pixels is not the only determining factor of detail. Motion blur, noise and optics also determine how good an image will look printed.
When creating a project, a low resolution warning will appear to indicate the minimum recommended resolution for the type of print or book you are making.