Just be aware that any international postage printed on line (paypal and click-n-ship) you are limited to the classes that you can send. You can't pre-print first class international postage.
When I ship to Canada, I prefer to use click-n-ship it's easier for some reason, and yes you will need to print out, 4-5 sheets. And your customs form is already on the label. Then you need to get a clear sleeve from your post office and the sheets are placed into that sleeve. So use regular copy paper and not peel and stick labels.
You can call your postmaster and ask they deliver a couple of these clear sleeves with your regular mail, so you don't need to pick them up at the post office. That way you have them when you need them.
And Tabitha is right, it's a lot easier to request a home pickup from your carrier than running to the post office. I rarely go to the post office anymore.