Obviously people moved to Canada during that time, but not at the levels required to offset the ageing of the population they already had. Hence the issue they are facing right now. It isn’t just about population numbers, it is about ensuring that the rising numbers don’t end up too old to work and contribute economically.What about loads of people who moved to US and UK in the 2000's and some part of 2010's and permanently settled there? Was Canada also allowing the same thing to happen during that time? Maybe if they did, then Canada wouldn't have to target "record" levels of immigration now when moving permanently to any other western country is pretty much impossible through study or work visas.
Alternatively, they could make Canadians just have more babies, which clearly isn’t happening.