Harley-Davidson produces motorcycles with engine sizes that can range from around 500cc to over 1,800cc. They are known for their larger displacement engines, particularly in their touring and cruiser models.
Ducati and Triumph, on the other hand, are more commonly associated with sport bikes and typically offer motorcycles with smaller to mid-range engine sizes. I recommend checking the official websites of the respective manufacturers for the most up-to-date information on their current motorcycle models and engine sizes.