Record in 1 channel or 2?
 

I just got a Shot gun Mic and boom pole. I'm curious if I should record in 1 channel or 2. I will not use the camera's mic when I use the boom mic. I have a Canon XL2.

P.S.

Standard Operating Level (SOL) is -20Db correct.

I'd go into both channels and set one 8 to 10dB lower than the other. Unless you're going to be recording a lot of shouting, I'd go in hotter than -20dB. -20 is a good measurement for pro-quality digital recorders with very low self-noise. The XL2 is not a pro audio recorder and should be fed a hotter signal to ensure good ratio of signal to noise. How hot is up to you.

I usually go into cams like this around -12, but I'm a sound guy and have a mixer with good meters so I can back off if a scene starts to heat up. The simplest answer is get a sound guy with a mixer to watch this sort of thing. Otherwise you'll have to just set levels the best you can and hope they're not too noisy or they don't clip the safety track.