Looking for boat ride around the canals in Venice

We will be in Venice three days between b2b cruises this fall and I would love to surprise my husband with a small boat ride/tour (maybe 2 - 4 hours - not sure how much you can see). Just the two of us or we could add two more if cost is too high. I'm just starting my research on Venice but so far have not come across any type of tour like this. Lots of walking ones.
I appreciate any help or suggestions where to search.
thanks

We were there a few months ago. As you may know there are many islands. The area where st marks square is is just one. There are many gondolas for hire and they are 20-25 euros per person for what seemed like 15 30 minutes. Not so much a tour of anything but an experience. tours-Italy.com and viator.com may have what you are looking for. My experience with them is they are good but represent a markup on what you can arrange on your own. What you do get is piece of mind that you have a reservation and will get it accomplished. Perhaps your hotel could point you directly to a provider. We didn't do it as we only had 1 day is to take a boat across to other islands.

Thanks for the reply. We will be on a cruise ship which overnights in Venice the last night. We are staying on the ship for another cruise and that one overnights in Venice the first night so no hotel. I am really looking forward to three days there.
I will check out the sites you suggested. Thanks, Sandy