I don't think it will be possible for Manchester united to play all three clubs to win the cup. Manchester united might only play two out of the three clubs which I don't see it as a big challenge for Manchester united. They have succeeded the toughest club which is Barcelona.
With Manchester united present form,the team will be able to defeat Arsenal in any encounter. Arsenal won them in EPL recently doesn't mean Arsenal can win them again. I saw that game that Eric Hag gambled with that match because he was looking for a draw but it turned to be a do defeat. As for Roma and Juve,it won't be a easy for Manchester united to win these two clubs but I think they have more advantage of winning these two clubs because they can't be predicted anymore after their victory over Barcelona.
With Manchester United present form, they could play and win anyone, Arsenal included. The fact that Arsenal had won them earlier in the premier league doesnt mean they can win them again. Manchester United has gotten so much better.
I believe Manchester United pretty much has the drive and pressure to go ahead and win any team they encounter. And now that they have got the right leadership in the form of the coach Ten Hag, its just a matter of time before the trophies come rolling in.