Based on history, the Bucks and Mavericks will be going home on Sunday. Since the 2011 postseason (not including the bubble) home teams are 22-10 straight up in Game 7's, a staggering 68% hit rate. With that in mind, home teams are just 16-16 against the spread, as the series goes longer and the number becomes more defined, there's no edge betting the spread.
However, favorites of 5 or more (which the Celtics and Suns both are at WynnBET Sportsbook) are 14-10 against the spread, slightly above average and are 19-5 straight up.
There is definitely some evidence that the home teams benefit from their home court in a Game 7, but that number has been trending down lately