Kids get so few choices - I agree with giving him a little control - with "parent approved" conditions. Buy TWO fun toothbrushes. Brushing teeth is NOT an option - choosing which toothbrush (or toothpaste) to use, IS. (The cost of a second toothbrush is way less than I would pay for peace at bedtime!)
We had some luck with singing a song while the kids were brushing. The same song, every time. When the song was over, the kids knew their turn was over, and it was Mom's or Dad's turn to brush. And while we did it, we sang the same song. This way they knew there was an end in sight.
Toothbrushing is always done in the bathroom. With both kids, there were some fights early on, but eventually, the kids knew this was a battle they were not going to win. They learned the difference between 'the hard way' and 'the fun way' - we made sure to define that.
There is still some hesitance for toothbrushing, since both kids know it is the start of the bedtime routine. We threaten them with zerberts (raspberries), or tickling, or 'race' them to the bathroom. Goes back to trying to make it fun.
Good luck!