How do you go about brushing your toddlers teeth?

My son is 3.5 years old and brushing his teeth is by far the hardest battle.

We have tried what feels like everything: letting him brush our teeth while we brush his, "racing"(I brush one side and he brushes the other), different toothpastes, different tooth rushes (even the one they put in their mouth and move back and forth. I stopped using it cuz they aren't as good.), timers, having him brush his own teeth and then brush them a bit more later, even rewards.

My husband doesnt do teeth brushing time anymore because he knowa he doesmt have the patience for it. My son knows it's going to happen no matter what at this point but he still pulls away, closes his mouth and sometimes even cries. I know im not brushing hard and will spend what feels like forever trying to get his teeth brushed.

How do I make brushing his teeth a less terrible time for all of us?

P.S. we took him to the dentist and he does have 2 cavities they plan to fill in the next couple of weeks.