The Montreal Gazette reports today that according to Radio Canada and LCN (French language news service) the mosque attackers are Alexandre Bissonnette and Mohamed Khadir. It has not yet been revealed whether they claim to be Muslims or not, but this is looking more likely.
While I cannot tell what brand of mosque the Islamic Cultural Centre of Quebec contains, its website mentions that the lead imam was trained at the University of al-Madinat al Munawarah in Medina, Saudi Arabia, which is known as a bastion of Salafi ideology (known for their ties to early Islamic, hence extremist beliefs). That may or may not prove to be significant with reference to the motives of the attackers.
What the names of the attackers seems to rule out (especially that of the Moroccan killer) is that this was the work of a Western right-wing conspiracy group. More likely is that Mr. Bissonnette is a convert to Islam and that he was perhaps following the lead of his Moroccan partner. News reports indicate that one of the terrorists (who fled the scene) called police to turn himself in, saying he felt remorse over what he had done. So it sounds like one of the two was the instigator and the other a semi-willing accomplice. But of course I am speculating and could be completely wrong!
Again, time will tell.