A "main body" of work is the most authentic and significant line of work within the franchise.
The consensus is that the Dragon Ball manga is the most authentic work as it was directly penned by Toriyama, so all the events in the manga and the matching events in the anime would be considered "canon" as well.
Any event in any of the animated work or video games that did not occur in the manga that was not written with the help from Toriyama or contradicts the events of the original manga would be non-canon.
"Branches" goes against the concept of canon, as those "branches" would take place in an alternate universe separate from the "main body". They would be more akin to "what ifs", but made by those who were allowed.
Hypothetically speaking, if Toriyama confirmed that someone would continue the story of Dragon Ball (even without his help), the new author's work would be considered canon. If there is no confirmation, then those works would not be considered canon.
The problem isn't the "rules" of Dragon Ball canon, the problem is that there are multiple sequels that Toriyama has been involved in produced after the end of the original story's run. What someone considers "canon" from that point would be more based in personal preference than what was from before that point. Frankly, that is not an inherently bad thing.
To refer to the biblical canon, there was (and still is) more than one canon of the Bible, one for each sect. Regarding the sequels contributed to by Toriyama (GT, Super, DBO), Dragon Ball indeed has multiple canons, and the claims that there is only one is mainly a subjective declaration now.