He'd have to get elected to parliament first. As you mentioned, the NDP came close to winning some seats in the 1960s, but never actually did. So the question is, would he have been popular enough to win in any seat?
Mount Royal & Notre Dame de Grace are your best bets. The NDP nearly won 30% against Trudeau in the former and only lost by about 12% in the latter. I think NDP-Trudeau would have a chance in either of those.
If he couldn't get elected in Quebec, he'd have to get parachuted somewhere which has it's own problems. I doubt Trudeau would do well in a blue collar NDP riding. Perhaps they could've ran him in a downtown Toronto seat.
