The best way is to go to a place that has Canada geese and sit down and listen to them and try to match what the birds n the water do when they are calling to other geese in the air, you will be able to pick out different calls, also listen to them when they are on the ground or water talking to each other when feeding, that is also a useful call when finishing them over the decoys. The next best thing is to buy a recording of one of the folks who make calls and give instructions on how to call. Better yet do both. I would't put too much stock on the geese that swam near you because they probably are not real scared of people and you want the birds to come to you in the air, not on the water.