I don't see how such a coalition would be so crazy. All four parties involved basically have the same stance on almost all social and economical issues, bar a few exceptions (Quebec's independence being the main one).

I mean, France had been governed by large leftist coalitions (from center left to socialists, communists and greens) quite a few times, and it wasn't worse than your average right winged government. Now, Canada isn't France, but well, I wish them good luck for kicking Harper's ass. He deserves it.