No, STO is not canon. The story line of this game is absolutely absurd, and would require a reworking of already established canon in order to make it work. This game is pure fan service designed to coerce you into making micro-transactions.
The inclusion of voice overs is to provide you some sense of immersion while your federation toon stands on the bridge of his/her dominion ship holding a bat'leth, while their liberated borg, Breen, Jem'hadar, and Romulan bridge officers man their stations. I think Star Trek Encyclopedias across the world would spontaneously combust if they ever tried to make any of this canon.
I've never understood this argument for canoninity. I'm not arguing that STO is canon, but being made by fans certainly isn't what determines this. If CBS made a new ST Series today, you can bet your life there'd be fans involved in it's production. Even on TNG, Whoopi was on the show because she was a fan of TOS.
And by that logic, the JJ movies ARE canon, because JJ isn't a ST fan?