Whale season is the end of November thru May, so if you are here in March your chances are pretty good. BUT there is no 100% on getting to see the whales underwater. According to laws we have to stay a minimum 100 yards (it is 100 yards, right?) away. If anchored and they come your way while in the water...that's ok.
As sound travels very far underwater you have good chances of hearing them though...awesome experience! Also during the season, if your lucky, you will get to see them breach or filp a tail or fin.