I believe groundhog, woodchuck and marmot all refer to the same animal, at least where I am they do.

From Wikipedia:

Groundhog
Rodent
The groundhog, also known as a woodchuck, is a rodent of the family Sciuridae, belonging to the group of large ground squirrels known as marmots. It was first scientifically described by Carl Linnaeus in 1758. Wikipedia
Scientific name: Marmota monax
Family: Sciuridae
Trophic level: Omnivorous Encyclopedia of Life
Mass: 3.9 kg (Adult) Encyclopedia of Life
Higher classification: Marmot