I wouldn't assume that they'll definitely get Grealish. Villa have hugely ambitious owners and have Grealish under a long contract; they'll do everything they can to keep him.
As for whether Grealish wants to go... Man City is definitely a step up, but perhaps his experiences at the Euros may impact his decision. For England he is merely an impact sub, which is likely the role he'd have for Man C. Would he prefer to stay at Villa, who are improving each year, and be a guaranteed first teamer?
They managed last year to win EPL without the need to use Aguero who barely played last season and know left the club for free to Barcelona,
It's true that Man City won the league last season but their scoring record dropped from 102 in season19/20 compared to 83 goals last year its their lowest in the last 4 seasons.
They managed to win without scoring lot of goals last season but I don't think that this season that alone will cut it their rivals are focused on getting back on winning the league so i think it will be more exciting to see Man City without Kane because signing him it will make them impossible to stop.