Typically, if you can take or check it on a plane, you can take it on a bike tour. So, generally, one bag under 50 pounds plus one carry-on bag per person.
It can vary from tour to tour, so check the "Included services" on the Dates & Prices tab of the individual tour for any restrictions.
For bike and boat tours, there is limited space onboard. Smaller, collapsible luggage is recommended.