Officially, none of them (not even novelizations of episodes and movies). There are 2 Voyager books, "Pathways" and "Mosaic", that were considered canon by Voyager writers (because they were written by Jeri Taylor) but eventually ignored.
While the novelzations are sometimes rationalized as canon in discussions, they are not because these books contain additional information that was not presented on screen. The information is treated similarly to facts read in scripts but not seen.
Books written by the cast and crew are often called "quasi-canon" since the information was likely used to motivate a plot or simply waiting for an opportunity to be shown on screen, but is not fully canon. Quasi sources include the various Technical Manuals, Chronology, Encyclopedia and similar books.