Princess Cruises spokesman Brian O'Connor announced the company was saddened to discover the humpback whale and it was unknown how or when that happened as the ship had felt no impact.
It was still unknown whether the whale had been alive or already deceased prior to becoming lodged on the bow.
Navigators had spotted no whales close to the ship as Grand Princess sailed overnight towards Ketchikan, near the southern tip of Alaska Panhandle, north of British Columbia.
The mammal might be a juvenile. Ketchikan Daily News reported it was about 6 metres long.
Grand Princess was starting her 3rd day of a 10-day round-trip voyage that originated in San Francisco.