Not all geese are created equal!
If hunting only Greater Canadas (8lbs & up) use steel BBB's in a 3" shell or #2 or BB Bismuth, or #1 in Tungsten Matrix or #4 or #2 Hevi shot.
Lesser Canadas, Snows & Specklebellies, ( 4-6 lbs) #2 or #1 steel or #4 or #2 Bismuth or #3 or #1 TM or #4 hevi shot. What's right depends on the distance you'll take a shot, the choke of your gun, and what patterns best in your gun. In most cases, Modified choke is best but IC or IM may be better. Full choke is almost never best except for pass shooting with TM shot. I have used ALL these combinations on a great many geese. Now I normally shoot 12 ga. 2-3/4"#1 Fasteel for everything, out of a modified choke, for birds over decoys. In a "normal" morning of field shooting in Saskatchewan we have mallards and pintails at dawn, (and some Specks if we're lucky), Lesser Canadas a little later, followed by Snows & Ross', then the Greater Canadas show up if we haven't limited out by 9am. Don't stretch you range too far and the Fassteel #1's will do the job for everything within 40 yards. If you need to stretch range or specialize, see my previous suggestions and PATTERN YOUR GUN!