Yes the model in Sisko's office is canon. If it shows up once or a million times its still canon. Don't think that's in dispute. Is it the Daedalus? Well, the canon has nothing to say about that. Until a ship with that configuration and name shows up on screen it remains a nameless ship model in Sisko's office. The Discovery people could apply the name to a totally different design and at that point that design for the Daedalus becomes canon.Speaking of some things people don't get…
Just how many times something has to be shown onscreen to be considered canon?
Once?
http://www.ex-astris-scientia.org/articles/daedalus/daedalus-themaquisi.jpg
Twice?
http://www.ex-astris-scientia.org/articles/daedalus/daedalus-afterimage.jpg
Thrice?
http://www.ex-astris-scientia.org/articles/daedalus/daedalus-inquisition.jpg
Please stop me when you've had enough.