Well Reach could very well be canon, but Bungie tried to make a connection with Noble team and the larger halo universe by putting Dr. Halsey in the game. In the game, she knew that Noble consisted of Spartan-III's, but in the novels, she doesn't even know III's existed until the time Halo 2 is taking place, so that's half of the evidence. And in Reach you were supposed to bring Cortana to the Pillar of Autumn, but in the books she was aboard the ship the whole battle. These books were made before Reach, and they support the story of the original Halo trilogy, so they are definitely canon, and since Reach has these contradictions, it is non-canon. You can acknowledge that it's non-canon and completely disregard the games story, or you can do what I do and believe that Noble did exist in the Halo universe and did die fighting on Reach in these ways, but Halsey and Cortana weren't there. Hope this answered your question