In terms of how the data is collected, the first thing to understand is that Statistics Canada is a very important source of information when it comes to job vacancies. That said, a vacancy does not necessarily mean that there is a shortage. Statistics Canada carried out a census of employers to find out how many vacancies there were in the country. It is normal to have vacancies. They may indicate that a business is growing, that employees are retiring and that staff needs to be hired.
Currently, the number of vacancies is a little bit higher than it was before the pandemic, as you have seen.