Rerailing this thread, should Venice have a Canals UB rather than a Great Galleas UU?
Nope. Canals may be what Venice is famous for, but they aren't the canal master. Amsterdam has more canals than Venice does. So why not give it to the dutch?
Plus, Venice may be famed for its canals but it's not like they actually do that much. They basically function as a different way of getting around the city. If anything they are annoying and hampering because they take longer to navigate. Sure they look cool and it gives Venice a great feel, but that's about it.
As a replacement aqueduct that's a big no for me. The canals don't encourage growth, as they don't provide fresh water to the city or anything like that. There isn't much that the canals really do that's different in a game representation, perhaps offer a tourism bonus??
Either way I think that the Great Galleas will offer FAR more. Early game Venice is going to have PLENTY of time to pump out other units as they are going to be growing quickly (no settlers) and building quickly (because, again - no settlers). They will need fewer workers, as they don't need to divide attention between cities etc.
The Great Galleas will allow Venice to be a military threat to coastal neighbours very early. Grab a city-state, or hold back a coastal rival (or take their cities) and boom Venice is charging ahead.
Personally I think Venice is going to need a period of aggression to not be overwhelmed, and earlier is better. The later their period comes the less their OCC goes from being a military advantage to being a big disadvantage. That will happen early and Venice need to be aggressive in that time. Anything after the Galleas is going to be too late to be effective.