While I'll accept it can be done as many times as one has focus tokens, I doubt it is squad wide. I'm pretty sure the 'you' here is referring to Kanan only.
Look at Garven's ability:
Or Wedge's:
When attacking, reduce the defender's agility value by 1 (to a minimum of "0").
Or Horton's:
When attacking at Range 2-3, you may reroll any of your blank results.
All use similar wording regarding "When 'X', you may 'Y'" but nobody plays these ability as squad wide. I am positive Kanan's is the same.
The issue that you don't seem to see is that the X is very, very different. "When an enemy is attacking" is not nearly as specific as "When attacking/defending".