Here is a link with lots of goose talk on it. Very helpful and very free.

http://www.callingducks.com/talk_goose_main.aspx

Click on the caller, or click on the vocalization. You'll hear a calling demo, and often read a write up on when and why geese make those noises.

If you want to call Canadians.. don't forget to dial 11 and the international code.