During his Reddit AMA, Matalas made a number of interesting comments about what he had wanted to do or envisioned but ran out of time or money.
Among these things were that Ro Laren was supposed to return at the end as the Changelings had beamed her off the shuttle before it exploded. He also commented that he hoped that Wesley and Jack would have met at some point before Jack got posted to the Enterprise.
Would you consider these things canon?
Creative intent that clarifies what is on screen is canon because what is on screen is confusing is canon. Expanding the story beyond the scope of what is on screen is not canon, but certainly worth knowing and keeping mind in absence of another explanation.
Example (actually from David Blass): the Enterprise E, or an Enterprise E style trophy case is in the Conference Room of the Enterprise D, replacing the Season 3-7 wall when you look in through the window. It is clearly visible in stills of the CG.
Is it the Enterprise E's? That was not clarified.It could just be the same style case.
But Blass recognized the case as being there. It is there in canon now. Geordi made a change to the Enterprise D. We can speculate that because the Season 1/2 conference room wall was dated and the Season 3-7 one was ugly.
Better examples:
Q: Is Admiral Shelby the commanding officer of the Enterprise-F?
A: No. In Star Trek, Admirals almost never permanently command starships, and no admiral with as many pips as Shelby ever has. Per Matalas, she was there in her function as master of ceremonies given the occasion. That is canon, because we never hear or saw anything like "that's Shelby's ship". Just her in the seat, which does not necessarily imply permanent Captaincy.
So is the Star Trek Online Andorian captain now canon? No. Matalas says he imagines a canon version of him is the CO of the Enterprise-F, but we haven't seen him. So the captain of the Enterprise F is unknown.
Q: Is Shelby dead?
A: We don't know. She got shot twice in the chest. Matalas says she may be alive. We never saw a body. Creative intent is "may be alive", but visual evidence lacking for or against, therefore canon would be "Status: Unknown".
Q: Where is Jurati-Borg, unmentioned (in that context) in Season 3.
A: Matalas says guarding the Season 2 Transwarp conduit. We can say that's canon, because that's where we left them off at the end of Season 2 and what they said they would do. We have no reason to think that would change. Matalas is clarifying, really restating, what the Season 2 end of season status was.
Matalas is worth listening to because creative intent ALWAYS informs context of what we see that is often getting harder to make out on screen nowadays in TV shows and movies (in general). But the canonicity rules haven't changed. A clarification is a clarification and is canon, but an elaborating is not cannon. Which is what is really a case-by-case thing.