At1st level Eldritch Knight obtains the following ability:
Diverse Training: An eldritch knight adds his level to any levels of fighter he might have for the purpose of meeting the prerequisites for feats (if he has no fighter levels, treat his eldritch knight levels as levels of fighter). He also adds his level to any levels in an arcane spellcasting class for the purpose of meeting the prerequisites for feats.
While his Spells Per Day ability specifically explains what to do in case of multiclassing with more than one Arcane spellcasting class, this ability does not.
Does the Eldritch Knight add his EK level to any arcane spellcasting class he also has for the purpose of qualifying for feats? If not and only a single class gets that bonus, can that class be different from the one benefitting from Spells Per Day? Finally, can he add some of his level to one and some to another?
Considering an example: a Magus 3/Wizard 10/EK 2. Is it possible for that character to take the Extra Arcana feat and select Broad Study (Wizard) while advancing to the 3rd level in Eldritch Knight?