I'm going to have to vote for Winnipeg for obvious reasons, but a quick look at the
components of growth and Winnipeg has a strong advantage over Quebec for international migration (16,000/yr versus 6,000/yr for Quebec), but a massive disadvantage over inter-provincial migration (-7,000/yr versus ~0 for Quebec).
Winnipeg has much larger population growth AND population loss compared to Quebec, so it's difficult to say if the large population influx into Winnipeg will continue to be significantly larger than the population outflux over the long term. I get the sense that the more people that move to Winnipeg, the higher the outmigration rate several years later due to it being a "landing pad" for immigrants, poor state of infrastructure, or dissatisfaction with the weather.
While Winnipeg's own population projection puts the population at exceeding 1 million 25 years from now, it's difficult to say if Winnipeg's "big numbers in, big numbers out" growth will be make it the winner over Quebec's "slow and steady" growth.