Let's start with Main Street, which would now be Mickey Avenue, as in Shanghai Disneyland. This land would be themed to Mickey and friends, of course, and it would add more IPs. The place where you can meet Mickey is now home to all of the Sensational Six. Don't worry, the railroad's still here. It's just that this land doesn't have a turn-of-the-century theme anymore.
Onto Adventureland, which has seen some changes. The Swiss Family Treehouse is swapped out for the Adventureland Treehouse from Disneyland, and the carpets would still exist. But unfortunately, the Tiki Room wouldn't exist. Instead, a new show themed to Moana (retelling the movie) would replace it. The Jungle Cruise would still exist (Disney's not that evil) but with more ties to SEA and random Disney character cameos. Pirates would still exist, except that it would be entirely based on the movies (and it uses the Shanghai ride system).
Frontierland isn't really unrecognizable, but in a way it is. First of all, Tom Sawyer Island wouldn't exist, it (and the Rivers of America as a whole) would be replaced by the Cars themed experience that they're adding in our world. Tiana's Bayou Adventure would be built, and Big Thunder Mountain wouldn't be built. It would be replaced by a coaster themed to Toy Story that only vaguely fits “Frontierland” (it would be themed to Woody's Roundup and have a design more suited for Fantasyland. The shooting gallery obviously wouldn't exist, and neither would the Country Bears (sadly). The latter would be replaced by a show featuring Mickey Mouse and friends (and possibly Toy Story characters too)
See what other changes are made in the next part.