If I may be so bold as to give my thoughts. I've always looked at Star Trek as a very fluid universe, accepting of so many different roads even if they intersect from time to time. I mean that's why we can have so many stories of clones, alternate realities, multiverse theory, time-travel, etc all in the overarching realm of Star Trek. In terms of canon, it really is anything that is produced under license by whomever owns said license. Whether that be NBC, CBS, Paramount, or whoever picks it up decades and centuries from now. All of it is canon since it is all Star Trek (whether it's personally enjoyed or not). As for continuity that is really up to what productions want to carry over if they wish to at all from other productions, and what each person watching wishes to accept as an unbroken space of narrative. In the end every constructed highway of story is real and rooted. However everyone is free to choose which ones to take and which ones to not. Especially considering a lot of them cross from time to time. The universal web that is Star Trek.