Shot size for a field hunt?

[tth_12032]

I am going on a field hunt at Bittern Lake Lodge (compliments of Hunting for Tomorrow and Alberta Professional Outfitter Society) next week. I am fairly new to Alberta and haven't gone for geese yet out here. I assume there will be primarily Canadas but maybe some speckled bellies and snow geese?

What shot size do you guys use in a 12 gauge for this situation? I have a standard 3" chamber. I do intend to pattern my gun this weekend but thought I'd hear your thoughts first.

Thanks!