It's a ridiculous act by a ridiculous fan in a place where ridiculous and dangerous things seem to happen way too often.
But, MLB can't prosecute anyone and it cannot create criminal sentences from whole cloth in the Province of Ontario and the City of Toronto if the laws there don't allow those sentences. So, if the most that conduct would get is a light felony that brings little or no sentence, there's really nothing within MLB's power that can change that.
MLB could and should (and almost certainly will) insist that the authorities press full charges if they can identify and arrest the culprit. I would hope that MLB is offering any and all footage from the game that might shed light on who the culprit is.