To answer a few questions - I have been doing this for three years.
Yes, USPS will deliver supplies to Canada.
You do not need the address on the manifest, just an item description, amount and name ... you do need an invoice. The customs guys can take your stack of invoices - the last time it happened to us was almost 2 years ago.
I don't know about the Canadian return address, I use an US address. We ship three times a week ... it's just easier all around. Besides for the US MO's and checks - you can gather them at your box and deposit into your bank ... you don't have to specify anything special for your US customers (like no green postal MO's).
The 3.85 is for a lb in $US - when I do an auction I have a fixed shipping calculated to FL. If you go to www.usps.com it will tell you what the shipping cost is. For most of my products I use a Flat Rate Envelope (3.85) anywhere in the 50. I can usually stuff about 3-3.5 lb in one - It can't be to bulky or the postal employees will try everything to destroy them.
Encidia - reasons to use. If you ship over $1000 US a month, use your PayPal card ... it's really "free" (I use the premium service - hide the postage add some handling). All classes of mail are supported - I even ship to Canada in Small Global Priority envelopes (up to 4lbs for $4US). It's faster and cheaper than CP. If needed you can "self insure" with U-PIC ... it's cheap insurance and you can still leave your packages at the back door of the PO. If you have a webstore, you can still use Endicia ... it has nothing to do with eBay.
For the customs amount - that's $200 per person (it's their personal excemption). You can have any amount total for the manifests.
Hint - Photocopy several copies of the manifest. Then fill in all the stuff that is standard. And make several copies of this. If you are shipping lots of the same thing ... maybe Price labeller or something ... fill in the description all the way down the list ... that way you just have to fill in the price (no shipping) and the persons name - if you don't fill up the sheet just cross out what your not shipping. You can submit as many manifests as you want.
Todd, I think it's still worthwhile getting the decal (it's based on your vehicle, so you'll have to use the same one all the time). I don't know if they told you this ... but you can use the far right lane ... really slow down as you pass the booth and go and park under the canopy. I also have a stash of supplies (no matter what the web site says it can take a couple or three weeks to get them) - I might have enough to get you and
labels going until they arrive. Give me a buzz at (604) 644-9000 if you need some ... I'm in North Delta.