I was thinking you could do this in a single tank might not be as cool but for me I dont have two tanks close together. Just have it from one side to the other.
There is a bridge thing sold commercially and was kind of cool for kids. If you go to www.oscarent.com and look at the Aqua Trail. Its a cool concept, but I would want some water flow in there no matter the size.
to get a current in there is easy all i do is have a powerhead in one tank and plumbed the outake to the other tank so i move about 200 gph trhough mine
its really easy to make one i made my first one out of an old 2.5 gallon tank and if you want super cheap and easy make it out of pvc i know it wont be clear but it would work