Primarily, all dogs are individuals and we all know a huge number that don't comform to breed expectations. [looks down on the ground at the world's laziest springer and fondly remembers the world's most chilled out and tolerant jack russell]. That said, someone, somewhere made breeding choices to encourage behaviours in ancestors and so they are more likely (not guaranteed) to occur in some breeds than others. e.g. you don't get as many terriers with only the first bit of the hunting sequence as you do collies (see, turn to face, stalk, chase...... catch, bite, kill, eat).
Even if all dogs did confirm to breed expectations, all breeds have 'good' and 'bad' and often the thing that determines if a behaviour is good or bad, is simply the setting in which it happens. And it often helps to think of the setting it was MEANT to happen in to understand it.
e.g. Presa Canario's are originally guarding and herding dogs and there a few breeds that attempt to mix these two purposes. However, their specific physicality suggests guarding was more important than herding. Otherwise, I expect they'd be smaller and lighter.
What does it take to be a good guarding animal?
- A short socialisation window. You need an animal that quickly learns who are the good guys and then stops trusting anyone outside that definition. Gurading breeds appear to have shorter socialisation windows than other breed types. That said, the window is never fully closed - though it gets harder and harder to sneak anything through
- The ability to do nothing all day long. A good day for anyone with something they want to guard, is a day where no one even tries to attack or take it. This will be most days - so you need a dog that will sit and wait rather than get bored and go off and do something else.
- The ability to move into action very quickly and with little warning. No good barking from a distance when wolves are after your sheep. They'll be off with a lamb before you know it. You need a dog that is going to get right up in that wolf's grill without hesitation.
- The ability to think independently to some degree. As above, a guarding dog that waits for instruction is probably not much good. So they need to be prepared to do what it takes in the heat of the moment, whether or not a human tells them to.
So, here, we have the bare bones of the breed and in a home setting it may look like:
- Loves the family and is very tolerant with them but very mistrustful of strangers
- Average exercise and entertainment requirements, so very undemanding.
- But not always easy to predict if a threshold is crossed.
- May not adhere to training when it counts, i.e. when over stimulated/excited/worried
Layer on subsequents breeders breeding for dog fighting and you might also get a mix of...
- Acceptance of rough handling from humans with little attempt to use aggression to stop it
- Fear demonstrated as aggression towards other dogs
But they are all just theories. Primarily, a dog is an individual and should be judged as such, even if breed history is used to try to understand behaviour you see. The physicality of a dog is useful data because a) you may not want a dog you cannot physically restrain if needed and b) that physicality gives futher clues as to what behaviours have been selected for in past generations.
I realise the OP has already made a decision on this specific dog and it's probably makes sense, due to the lack of history knowledge which would help figure out which of the above behaviours/tendencies this specific dog is likely to have.