450,000 by 2026 sounds like a believable number to me. That's what my guess would be anyway... 440,000 - 460,000 people by 2026.
It's great Halifax has passed 400,000 population. Now the half-a-million mark is the next hurdle. Although alot of work needs to be done to get the city up to par to support that population.
Things like this don't help either:
Halifax Violence on the rise