I may be in the minority here, but it doesn't bother me for fans to look ahead. Players, staff and coaches obviously can't, but I don't see any reason why we can't. That's what this forum is for.
To answer the OP, I'm a little torn here. I love the way this team competes, stays together and believes in itself. And we have homecourt advantage, which is a perk. I also think that we may be the best-suited team to guard the Cavs perimeter players (including LeBron) in the entire league. Smart, AB, Rozier, Crowder and even Jaylen Brown can give us good minutes guarding Irving and James. As others have said, the Cavs aren't great defensively, so scoring shouldn't be a major issue as long as we're shooting well.
What concerns me the most is the other end of the floor. I think we have the players to make the Cavs work on offense, but they're loaded with sharp shooters. When those guys are on, which is usually the case, it's basically pick your poison. I know others have said that the Cavs aren't as good as Washington inside, but Love and Thompson scare the heck out of me on the boards. Cleveland is tough enough to force into a miss as it is, so any second-chance points we give up will be crippling. This is where I think we're in trouble, as rebounding is a major weakness of ours.
I think our best chance for success defensively is to force James into long 2's and/or 3's (in other words keep him out of the paint), don't let their role players get open looks from outside, play phenomenal defense on Irving, and rebound like our lives depend on it. I think we can do those three things for stretches, but can we for 48 minutes?
Lastly, I've brought this up in other threads, but when you're playing against a team with LeBron on it, you have to account for the officiating factor. Not only will we likely get completely screwed by the refs in every game in this (still hypothetical) series, but it'll likely resemble a WWE match due to the absurdity. Welcome to the NBA of the 21st century. So just being as good as the Cavs (which I'm not sure we can do anyway) won't cut it - we'll have to be significantly better than them on four separate occasions. While it's possible, I don't like our chances. As of today, I'd pick Cleveland in 5 or 6.