How do I substitute rehydrated garbanzo beans for garbanzo beans from a can?
I'd assumed the beans were cooked, not just soaked. Assuming they are cooked and not just soaked, the difference in taste could be due to canned beans' higher sodium content. Salt preference differs wildly across individuals and even across time for the same individual. There is a rich literature on this, including (sorry new user, so had to remove the URLs): 
http://www.ijpp.com/vol49_1/99_102.pdf.

It may be the case that you have a high salt preference. In that case, just add some extra salt to your hummus from dried beans.

Opinions on the quality of hummus from canned vs. dried garbanzo beans are a personal matter, but note that some (myself included) prefer the latter.

There are, in fact, differences in the hummus from dried vs canned beans, nutrition being one:
http://humus101.com/EN/2007/03/28/hummus-nutritional-value-dried-vs-canned-chickpeas/.