When my DD started throwing fits about brushing her teeth I did a few things...
If she bit me, I would pinch her lip, or push down under her tongue. (not hard, but enough to be uncomfortable. It only took 3 tries before she stopped, and she has NEVER bitten since...)
When she tried to bite the toothbrush, or to clamp her mouth shut, I would stick the toothpaste tube in her mouth... (we had the kind with a fat tip, and I would place it between her front teeth so she COULDN'T close her mouth.) That also helps with the breath holding... It's pretty hard not to breathe when your mouth is wide open!
When she fought too much, I would lay her down on the counter, and get them brushed.
She only fought me for a couple of weeks... Once she realized that it wouldn't get her anywhere, she stopped. She is 27 months now, and never fights me any more....
THAT SAID... have you tried any of the 'fun' ways to get him more interested? I used to let her hold MY toothbrush, and brush my teeth while I did hers. Or I would tell her 'open wide! We gotta get those dinosaurs out of your teeth!' (She loved dinosaurs...) This was when she just wasn't interested, and not actually fighting though...
Also... we got a cheapie electric toothbrush. ($5.00) My DD LOVES the way it buzzes, and I feel like it does a much better job getting her teeth clean than I can with a manual brush. :)