(Oh man, my sister is the real fish n chips aficionado, and she's a HUGE fan of Chinook's at Fisherman's Terminal, but that's a ways away).
How NORTH in North Seattle? Spuds at Greenlake has been making a respectable battered no frills fish and chips for decades. Ivars bought them awhile ago, but someone told me that the Greenlake branch is still independent (it's all hearsay, and while Ivars owns them, it hasn't seemed to change the food, so that's nice). It's an order at the counter type place.
Back when I lived in Greenlake (5 years ago) we really enjoyed Duke's for their breaded halibut and chips. Sit down, pricier restaurant. Again, I haven't been in 5 years, but it used to be good, and their chowders were great.
My only other north end recommendation (again, where I haven't eaten in 3 years, sorry my data is out-dated) is Scott's Bar & Grill in Shoreline. They used to have great fish and chips. But 3 years ago we had a bad scallops experience and haven't really been back. But it might have been just a fluke.
Good luck!