Yesterday, I shipped a #000 bubble mailer with 4 cards in 2 toploaders from Canada going to the US from the post office. It weighed 32g and it cost me 2.65$ as it was apparently a light packet (up to 100g) to the US. I've looked around the Canada Post site and for an item to be considered letter mail, it need to be maximum 5mm thich, so there's no way the bubble mailer can qualify. I've also been told by Canada Post on the phone that there is no way I can send my bubble mailer myself in a mailbox, I always have to go to the post office so they can weigh it. So basically:
Toploader in a plain white envelope Canada -> US: 1.10$ for < 30g, 1.34$ for 30g to 50g
Bubble mailer Canada -> US: 2.65$ for under 100g but you have to go to the post office.