You should be able to get different cruises with English guides. There are several companies operating harbour cruises, you don't need to book. Head to Landungsbruecken S/U Bahn station on either on the promenade or down on the floating landing you will see multiple companies offering cruises. You have the option of taking a Mississippi type riverboat or larger boat which typically take an hour or so with commentary in both English and German, or alternatively take a small boat that goes in and out of the docks via small bridges that the bigger boats can not navigate. There is also the option of taking a longer cruise (2 hours) that includes the canals round the old warehouses. The smaller boats tend to have dedicated English cruises, again ask before you book what time the English tour is. Price is normally between 10 and 15 Euro.
Just be warned, if you are easily sea sick the smaller boats do get affected by the wake of the bigger boats passing by!
You can also take the HVV ferry to Finkenwerder and back included in the price of your day HVV transport ticket. It has an open top deck, and bar! It also leaves from Landungsbruecken. Look at www.hvv.de