I'm not sure if this is an important match or not what is clear is don't be too confident on one side. Indeed, Manchester City deserves to be the favorite to win because they have a better history and statistics it's just that sometimes the unexpected can happen for example they play young or new players well this can mess up our predictions so it's better to wait a few hours before the match starts to see the starting lineup. By the way so far the sportsbooks Stake.com prefer Manchester City and both teams to score YES and over goals are still the favorites to place bets, I don't think both teams think about playing defensively meaning the fight will go on until the last minute and let's wait for the next 4 days.
City won't play purely defensively but it could happen that they control the ball all game (without trying to take risks, playing "for sure"), then United will have big problems to score a goal. So I'm not at all confident in BTTS. I'll probably just place a simple bet on City, as it will be a normal game (and not a game where City players have not had time to sober up from drinking in honor of the title) as I expect them to justify their status as favorites.
However it is community shield which doesn't have much importance but yet it is a derby match and so we expect it to have the derby weight. So, it will still be an interesting match and probably a win for the citizens.