Guardiola surely won't forget that Tuchel prevented him from winning the title that he and Manchester City awaited for long time, so this time the competition isn't between the players only. There's no doubt that this match is the most competitive one in this round, and supposed to be the most exciting. Manchester City seems to have a complete list with no influential absences, while Bayern have announced the absence of Choupo Moting, one of their outstanding players. However, they have many stars in the substitution list, but Tuchel might be forced to make some changes in the tactics.
I don't think so, they need to win with any result. Even one goal can help them. Bayern Munich knows how to counter attack their opponents, so Man City need to be careful on the defensive side. Nonetheless, if they decided to play an open match, that would not hurt them as the rule that counts the goal in the outside matches as two goals was deleted, so it won't differ if they received 1,2, or 3 goals. The only thing that can help them is to score more than their opponent, and I think they are able to.