Send him north, or northwest, or west. You won't be able to build bridges over the river until you get engineering (it's engineering, right?). Of course, that would only impede troop movement. Trade routes between the cities are a non-issue.
But still, I think it would be safer to search north or west first, so troop movement over the river won't be annoying. You never know when you might need to desperately move troops across the river. That extra turn used could turn out badly?[small]or maybe not?[/small]
Unless forests across a river still count for trade routes under The Great Warpath bonus, in which case my point is null.
[sup][sup]GO NORTHWEST!!![/sup][/sup]
EDIT: Oh yeah, build a monument. ^^
