Hello 'littlemice',
If you wish to sell to the US you must include a shipping fee. Otherwise your items will not show up in Search for folks across the border. Here's the official Word on it if you wish to see:
http://www2.ebay.com/aw/ca/201109221712382.html
It's really not that difficult, - you need a postal scale and a metric tape measure, both of which can be bought cheaply at your favourite hardware store. You weigh, measure, and go here:
http://www.canadapost.ca/cpotools/apps/far/personal/findARate?execution=e1s1
You need to use metric or else the numbers you get may not be accurate. Pick a zip code far away, like in Florida or California. Remember that old show '90210'? Well a lot of people use that zip because it is just about impossible to forget. After you sell an item, if it turns out the $hipping you charged is much more than the actual cost (if you print your label through paypal you get a discount) you can always refund the buyer some of the extra. Few things make people as happy as receiving unexpected money.
In short, you must include a shipping fee if you want to sell to the US.