If you had one dive to do in Nova-Scotia...

[Nehallenia]

Grand Narrows would fit the description of your diving.
Word of warning though: The current is ripping and if you're not comfortable with that, than better stay away.
More pics here :http://www.scubaboard.com/gallery/s...check=0&page=1&sortby=&sorttime=&way=&cat=500

True there can be some pretty serious current at Grand Narrows. Sometimes it is negligible, sometimes severe, and no-one has figured out how to predict it! The first time I dove there, we didn't go to the wreck because the current was too strong, just stayed around the bridge pilings where there is still plenty to see (marine life). That was my second dive after my checkouts. I thought holding the guide rope and flying in the current was great fun, so was surprised when we surfaced and the more experienced divers I was with were exclaiming about the severity of the current! The note of caution here is: make sure you dive with a local, experienced diver.