I actually worry about Arsenal to win the match against Manchester United even though in terms of interests I don't want Manchester City to win the four -season PL Trophy in a row.
I share the same view with you on this, about Arsenal being able to Win Manchester United in their fixture while Manchester City plays with Fulham. I don't think Fulham can beat Manchester City because their last 5 fixtures was a straight win for Manchester City over the Fulham club. Fulham never had the opportunity to win both home and away and now that the ManCity guys are more prepared, one won't expect anything less.
As for Arsenal vs Manchester United, I also see the last fixture against both teams and Arsenal gave them a 3 over 1 win. Will Arsenal be able to replicate the same efforts in tomorrow's game is what I can't say but hope for Arsenal to achieve to as to further accelerate their winning streaks.
I personally think tottenham is stronger than Manchester united as of now, and if Arsenal were able to beat tottenham, then I see no reason why beating Manchester united should be or appear difficult for them.
And speaking of the current game between Manchester city and fullham, Manchester city besting fullham is what I expect to happen, any other result like the game ending in a draw or fullham winning is not realistic and can only happen by luck.