Canaletto's interest and working choice was to represent the city of Venice he was living in at its best.
Canaletto's paintings of Venice are full of life, crowded with lots of different kinds of characters, priests, children, dogs, women (in elegant attires or working and carrying something), art sellers, elegant (rich!) tourists appreciating the sceneries, always ecstatic about the beauties of Venice, boats sailing, beggars, a whole world.
These details make Canaletto's drawings very intense, lively, but can we see it as real? Maybe. Anyway, due to how Venice was considered a tourist spot in those times, this is not surprising.
Canaletto used to experiment and prepare sketches of images of different elements that would be used for the final works. Nothing different from what most of other painters had always done, of course.
They probably served as a reservoir where he could experiment situations and then use or reuse them according to his needs.
Or just a testing for the right technique to display a person, or a situation: a scrapbook of usable material.
He really had an amazing skill in reproducing people with just a few touches, as we can see in these examples here: