Low Int really only matters to a magus for Lab Totals, and there are plenty of ways to bring them back up, from Puissant/Affinity with Magic Theory (an intuitive magus), to getting higher Arts, getting a focus, sticking to spells with Lab Texts you can get your hands on, and virtues like Inventive Genius (okay, bad name for a magus with -3 Int), Cyclic Magic (2 seasons),...
Here's a few concept:
The Urban and Urbane Jerbiton : +0 Int (or even less), Gentle Gifted, decent social skills, decent Artes Liberales/Philosophiae, and Mystic Choreography. Keep away from the most powerful spells, because you expect to cast in a Dominion Aura, and master every spell you can afford to cast slowly for Ceremonial Casting. Don't be afraid to use Spontaneous Casting, too. While you are at it, you might want to throw in Cautious Sorcerer and make sure to get a high Golden Chord with your familiar, which should be something innocuous in a city (cat, dog, dove, ...). You may not be the best spellslinger out there (in fact, you're way behind the curve) but when it comes to casting in a city, you'll be the best (because those strong spellslinger will have to back off from their favorite high-powered spells, what with the Dominion penalties and threat of a botch). Plus, you can actually live in a city and not get lynched by a mob of angry citizens.
The Brute (Bjornaer or Flambeau): high stamina, Tough, enough strength to wear armor, Puissant/Affinity with Parma Magica, maybe Giant Blood. Go for personal wards spells and a good Brawl of Weapon skill. Already mentioned
The master of spontaneous magic. This is a very difficult concept to pull off. High stamina (like +4 or +5), decent Artes Liberales/Philosophiae, and Life-Linked Spontaneous Magic. Don't even try to be a generalist, you need to specialize, and specialize in an area with a very flexible TeFo, for instance MuCo(An) (all the change into an animal spell), or PeVi (all the Unravel the Form spells). Get a focus, Puissant/Affinity with Arts, whatever you need to actually be able to cast those spells without resorting to Life-Linked Spontaneous Magic, which you need to keep in reserve for that one spell that will win the fight - and which can be pretty much whichever spell is best suited. Oh, and don't go for Diedne Magic, it's just not good enough when you actually get in a fight. Diedne Magic works best to give flexibility to a formulaic caster, what with casting halfway decent spontaneous spells without fatigue, it's just not good enough to cast high level spells on its own.