Viburnum trilobum is now most often considered a variety (varietas, var.) of Viburnum opulus (syn. Viburnum opulus var. opulus), the European Cranberry Viburnum, and it is designated Viburnum opulus var. americanum. Regardless of their names, the two can easily be confused. Below are a few differences gleaned from the literature:

Item (see images below)

V. opulus var. oplus

V. opulus var. americanum
(V. trilobum)

Author
  Petiole   narrow grove and large disc-like glands   shallow grove with small glands  Rehder, 1940
  Leaf pubescence  
  (use a microscope)		   usually present on lower leaf surfaces   usually lacking, except on veins  Cope, 2001

 

petiole, comparison
leaf underside, comparison
Species reference: 
Viburnum opulus var. americanum