If you're a canny investor, you know how to spend money to make money — that is, you're prudent, farsighted, and capable of protecting your own interests, particularly in matters of finance or business.
In contemporary usage, canny is a synonym for shrewd. Both words mean smart or sharp-witted, but they also suggest that someone is smart in a self-serving and possibly even tricky way. Canny is also related to the word cunning — another adjective meaning "wise," but with negative connotations. Uncanny is not the opposite of canny — it means "weird" or "unsettling."