Yes, there is a precedent for large animals inhabiting urban areas.
The typical mass of a adult American beaver is 20 kg. Feral dogs living in urban areas are known to exceed this at times. Although 20 kg is on the large side for dogs, some dogs are much heavier. Note that the article mentioned below specifically mentions that they may be any breed.
Are feral dogs present in cities? Yes, they are, and present a problem.
Feral dogs, as well as feral cats, are rapidly becoming a very serious
problem in most if not all of the larger metropolitan areas throughout
the world. Unfortunately these feral dogs, many which have been
abandoned by uncaring owners, have not only survived their life on the
streets but have also gone on to reproduce. This has further increased
the numbers and has lead to some very real health and genetic concerns
within these numbers. Feral dogs can be from any breed and most,
especially if born as feral puppies, are going to be mixed breed,
perhaps mixed breed for several generations.
Now, humans keeps abandoning pets which provides a continuous feedstock for wild animals, but as the article explains, such wild populations do breed. It is obvious that cities have dog-catchers and impound lots because of the population of animals that run loose.
There is no reason to doubt that ROUS could survive in an urban setting. Besides, have you seen how big the existing rats are in NYC?