What midi controller can I use with Sunday Guitar?

You can use any controller with Sunday Guitar as long as it sends midi. You'll want to make sure it's compatible with your Mac OS and MainStage version. 

Here are a couple controllers folks like:

• The Apogee Gio: it functions as an audio interface and a midi controller. It works fine along with MainStage and Sunday Guitar, you will just want to assign the buttons in Layout mode to control different aspects of the template. It does have an expression pedal input, so you may look into getting an expression pedal that you can use as a volume pedal, especially if you plan to do any swells or ambient guitar stuff.
• Behringer FCB1010: this one does have extra buttons and two expression pedals. it only hasmMidi in/out, there is no usb connection, so you will need a midi to usb adaptor, most audio interfaces will have this built in, but if not there are some cheaper adaptors/interfaces that will convert midi to usb available. It is not very “user friendly” and can take a lot to program. We recommend spending a few extra dollars to get the iFCB software by Wabbit Wanch.
• Line 6 FBV3: this has thirteen steel footswitches—five with assignable color LEDs—help you easily keep track of active amps and effects. Dedicated footswitches for bank up/down make it fast and easy to scroll through your presets. A built-in expression pedal with a wah/volume toe switch gives you even more control of sweeping effects. A dedicated tap tempo footswitch enables you to quickly synchronize time-based effects like delay and echo. And a chromatic tuner keeps every note sounding great.