Novelizations are on the same level of canon as any other tie-in novel. The fact that they're based on the script as a movie or an older version of the script doesn't make a difference. In his novelizations Alan Dean Foster changed almost every piece of dialogue, making it longer and more literary-sounding. There are also numerous plot deviations. For example, in the Alien novelization they find the singal transmitter and never see the Space Jockey, in the Aliens novelization Bishop never does the knife trick and in the Alien 3 novelization the ox replaces the dog and Dillon gets out before the lead is poured in.
The Alien Resurrection is the most faithful to the movie but even it clearly isn't based on the final draft of the script. Important pieces of dialogue are missing or changed, some scenes are in the wrong order, there are 20 aliens instead of 12 and some of the action scenes happen differently.
I've also heard that in the Predator novelization the Predator was some kind shapeshifter and even had the power to control animals, although I'm not sure this is true.
The AVP novelizations is different from the movie in every way. There are too many differences to mention. The most obvious one is that there are 5 Predators. At the end of the book, hundreds of aliens show up from nowhere.
Some people like to include elements of a contradictory story into their personal canon while leaving out other elements. I do this myself when it comes to things like encyclopedias or technical manuals but novels don't have any 'elements'; they are one whole story that can only be read from beginning to end. It can't be separated into elements in any logical way.