Will you be mounting the speakers under the soffit area of the house?
If yes, then I'd use a CL-2 rated wire.
As far as the wire AWG, much depends on how much of a load the speakers are, and the power applied.
If you have efficient 8 Ohm speakers and aren't going over fifty feet cable length, I'd use 12AWG.
I have 4-Ohm outdoor speakers, so I've used 10AWG and close to 65 feet for the longest run.