Anthropas,
Excellent choice.
I have the 12ga Ultra and 2 of the 12ga Trackers. All are dead on accurate. The Ultra absorbs more recoil due to its weight, enabling me to comfortably shoot heavier loads.
Anyway, as to the scopes, I would recommend a 1-4 power scope with a minimum 60ft FOV and 3.5" eye relief. The big FOV allows you to get on target quick in heavy cover or close in. Small FOV can make a deer at 15yds impossible to find quickly in your scope. I like the eye relief to be 3.5", but with a 20ga, you may be able to get away with less.
I like BSA Catseye 1-4x32--Big FOV and Big Eye Relief, inexpensive and pretty good optics.
Bushnell has several inexpensive but good ones too.
Simmons makes some too, but the eye relief is too short in my opininion--they have 4x32 with 5.5" eye relief, but the FOV is only 17ft, way too small for a slug gun.
The best one you can get under $200 is the Bushnell Elite 3200 1.5-4.5x32 which is available in the Firefly Retical which is cool. I have one on my TC Encore 209x50, and when I gets me another $200 free, I'll be getting one for my Tracker II.
I have a Nikon Buckmaster 3-9x40 on my Ultra, but I am using it more as a Target Gun at longer ranges than for hunting. I would never hunt with that scope on that gun. Others like them, however.