The Answer is:
Crookshanks
I am cunning, I am sly. ---
the basic traits of cats
I spy you with my tiny eyes. ---
if you haven't noticed, cats tends to do that with their eyes narrows, though some say they narrow their eyes when the light is bright. There are a whole lot of theories 
When all is fine and all is safe, ---
I open my large, big eyes. --- ---
cats widen their pupils when they feel safe and secure, and some say they do that when the light is dim.
I am always smiling, ---
If you look on the right side. ---
meaning that if you look on the sides of a cat's face, you can see that it is always smiling
Do not let that fool you, ---
My smile is just a lie. ---
when they're smiling on each side, doesn't mean they're meaning it 
I look outside and see a bird. ---
I wonder what it's like to fly. ---
I look down a stream and see a fish, ---
I let down my hook, haha! It's mine! ---
all of the above says that cats are really curious, and looks to observe the wilderness and dream and imagine