Canada

I spent a bit of time digging about and couldn't readily find information specifically about pensioners, but it was an interesting bit of digging to do, so thanks for the opportunity! I couldn't find specific data for the number of Canadian pensioners who have jobs. There is plenty about people aged 65 and up that I believe supports my assertion.

A nice high level quick find was [this 2017 Canada Census analysis from statscan( https://www12.statcan.gc.ca/census-recensement/2016/as-sa/98-200-x/2016027/98-200-x2016027-eng.cfm). There's a small section that includes some information that seniors with private income (savings or pensions) work less frequently than those with none but there's not really hard data there and it wasn't obvious to me which sources they were drawing from. A couple of the most relevant bits from the Highlights section are:

In 2015, one in five Canadians aged 65 and older, or nearly 1.1 million seniors, reported working during the year. This is the highest proportion recorded since the 1981 Census. Employment income was the main source of income for 43.8% of seniors who worked in 2015, up from 40.4% in 2005 and 38.8% in 1995.

One of the data sets published in 2023 is "Employment income statistics by industry sectors, Indigenous identity, highest level of education, work activity during the reference year, age and gender: Canada, provinces and territories, census metropolitan areas and census agglomerations with parts"

The link has the data filtered to those 65+, and the top row in the table shows that the total number of income recipients is 1,079,410. Per this 2022 report there are around 7 million Canadians who are 65+, which is somewhere around 14%.