I had the same struggle with my son around that age. I found that a trick worked only a few times, so here are a few different tricks that worked at different times:
1. He brushed my teeth first, and i brushed his.
2. Brushing in front of a mirror together and making funny faces as we brushed.
3. Brushing with him on my lap and me smiling and snuggling, to associate brushing with snuggles and other happy feelings
4. Watching a video about a boy who didn't brush his teeth and these "bad guys" came in with power tools and drilled the boys teeth and made him cry (it sounds traumatic, but it is a short song with a happy tune). Then we discussed all the bad guys in his teeth and what we needed to do to get them out of his mouth before they started drilling him (again, its all about tone...we tried to be playful with it)
5. Now (he's 6) I have him hum a long song while he brushes to make sure he brushes enough. usually we brush together and make silly faces to keep it fun, but sometimes he will brush by himself now.
6. We changed the tooth brushing to a different time for a while. When he was 2 and a half, he was resisting tooth brushing because he associated it with bedtime, and it was the bedtime he was resisting, more than the brushing. So we did it earlier in the evening and told him resistance meant he had less play time.
making it about a power struggle might be all part of the "fun" for your child. Force brushing will make it worse because he will put up a fight every night and just get bigger, stronger, and better at fighting you off.