The Liberal Party in Canada is left by Canadian, American, and international standards. It's fairly safe to describe it as "left-wing." Furthermore, they probably have more of what you would consider "genuine" leftists in Parliament than the NDP, so they are therefore the "main left-wing party." Besides, if we go by your definition, then the "main left-wing party" in Canada is not the NDP but the Bloc Quebecois, which would be awfully silly.
I think it's pretty safe to say that a) as a Canadian and b) a member of said party; I can say without talking through my ass that the Liberals are centrist and not left-wing. Primero, they're not members of the SI (unlike a majority of parties here). Second, Liberal leaders since Trudeau have been right-wing and Chretien was a right-winger by most standards. The Bloc Quebecois should never be interpreted in ideological terms given it's role, nature and makeup.
But I'll drop my argument now, and vote for the KPRF
