Hello,
you can specify different shipping rates to different countries. I usually put a Canadian, US and worldwide. Or if it's over 500 grams I use calculated shipping, this is using the weight and dimensions of the item and you still have to specify the method of shipping- for instance US can be air or ground. I personally never offer ground for overseas. Also make sure you add a handling charge, Ebay calculated usually overcharges on Canadian (so I don't put any handling charge) and undercharges for US and International (so I put $1.50) . It still comes out a little short but not as much.