Canada? Well, Ottawa is the capital, but nobody thinks of it as our first city. That's just for politicians and Remembrance Day ceremonies at the National War Memorial. Actual first place goes to Toronto.
The second city, depending on which half of the country people live in and what language they usually speak, would either be Montreal or Vancouver.
For
Canada it's definitely
Montreal, IMO. It's the second largest city in Canada, the hub of the French-speaking part of the country, and an major regional economic, cultural & transportation hub. It also played a much larger role in Canadian history overall and used to be (since taken over by Toronto) Canada's main economic and financial centre, where all large companies set up their Canadian HQ. Vancouver metro also has about 1.7 million less people. That's almost two Ottawas!
In the case of
Poland, the obvious choice is
Kraków, which was the Polish capital for about 600 years. As such it is a natural cultural and economic hub. It IS Poland's second largest city by population if you exclude the metro, but looking at metro population stats it
might appear that it has competition in the second city category (which it doesn't)
In the case of metro population the
largest city in Poland is Katowice (about 70km from Kraków!), with about 4.3 million people living in the Polish part of the Upper Silesian Metropolitan Area. It is basically Poland's version of the Ruhrgebiet, and just to be clear it probably makes sense to focus in on the 3M or so people who live in the officially designated Katowice metro. Warsaw's metro population comes in
second and Kraków places third. However, Katowice has a far less important and impressive city centre, it's basically a crapload of cities and towns all cuddling. Katowice by itself takes the spotlight - but each one of the cities around it has a city centre as well. It's not nearly as centralized as Kraków, which gets no cuddle action, and has a large tourist draw due to its history. Katowice gets more of a focus in terms of being an industrial hub, while both cities share transportation hub duties in the region IIRC. Overall Kraków outshines Katowice to a decent degree in the region as well as in the country.
Some people might point to Tri-City(Gdańsk+Gdynia+Sopot) or Łódź as a candidate for the Polish second city, but that's probably just local pride speaking. One of those is most likely the Polish third city though. Katowice is just too disjointed to be in the hunt for any of these titles, IMO, even the Tri-City area is a lot more compact with 3 distinct city centres and urban areas that are mainly connected.
Let me throw this out there though: What is Singapore's second city?