Sorry, maybe I wasn't clear It was what you meant by v2 I was asking, not v3, where there is no ambiguity.
There is only "one" Affinity v3, but there are "three" different Affinity v2s (as part of the Affinity graphics suite: Photo, Designer and Publisher), which Serif designed as an integrated suite but could be bought as a suite or as individual programs.
The take over by Canva combined these into a single program, so when you ask about the differences between v2 and v3, it depends on whether you mean Affinity Photo v2, or all the programs in the Affinity v2 graphics suite, because Canva Affinity only comes as a full v2 suite replacement.
Canva has tweaked some aspects of all the Serif Canva 2 graphics suite programs, but there are probably few significant changes to any of the individual v2 programs in v3, but a significant change if you are comparing, an individual v2 program with the combination of all three programs in Canva Affinity.
You mentioned in a later post designing book covers, so Canva Affinity 3, with its DTP tools, may be more useful than the tools available in Serif Affinity Photo 2, but no more useful than the tools in Serif Affinity Publisher 2.
Or maybe I've completely missed the point of your question :-(