I think IF Mackinnon can stay within 5 points or so of the points race, and the Avs make the playoffs, it's likely to be his.
He has other factors going for him besides just "top producer on playoff team" which, IMO, give him the edge. I'd say those could be summed up as breakout season, good narrative (highly touted prospect goes from disappointing to world beating in one season), and probably the flashiest highlights of the MVP candidates.
I'm not saying these things should matter for MVP voting, but that's the way I think the voters will think. Similar to the whole "can a non-playoff team player win the Hart?" question.