I can help - you started me down a rabbit hole.
This CMHC site has the Annual data reports back to 1921. (Obviously not in any useful data format, so I copied them one by one). They have starts, completions and under construction at the end of every year.
Starts and completions evened out over the decade are obviously similar. (Only in the 2010s are completions lagging starts a bit - presumably as buildings got taller and projects bigger, so taking longer to build). Here are the decade averages:
In the 1950s it was 115,000 a year, with 68,000 under construction
In the 1960s it was 150,000 a year, with 100,000 under construction
In the 1970s it was 230,000 a year, with 175,000 under construction
In the 1980s it was 180,000 a year, with 105,000 under construction
In the 1990s it was 150,000 a year, with 80,000 under construction
In the 2000s it was 200,000 a year, with 150,000 under construction
In the 2010s it was 200,000 a year, with 218,000 under construction
Peak house starts in the 1950s were in 1958 at 164,000. The 1970s had the most, with 268,000 in 1973 and 273,000 in 1976, but 2021 saw 271,000, so we're there again.
In terms of the numbers under construction, CMHC recently stopped posting data for the whole of Canada, only for CMAs, so the 353,000 under construction I noted earlier is just CMAs. The last 'all of Canada' number I could download was the end of 2022, when it was 378,000 units. That's easily the biggest number, ever, in Canada. It's more than doubled since 2011, when just 175,000 were being built. The previous peaks in the 1970s only saw 200,000 or so under construction.
So it looks like the development industry is genuinely firing on all cylinders, with more under construction than ever before, but they're taking longer to build, in many cases because they're more complex to construct in taller (so slower to complete) towers in many cities.