There is something similar, but as a consumer you don't have access to all the shipping options that an advertiser or publisher would have. Magazines would fit into the Lettermail/letterpost classification depending on destination. Specifically in the non-standard envelope rate.

Nothing but parcel rates are available online though.

The packages I ship normally will fit dimensionally within the parameters allowed for the non-standard lettermail. However since I process everything online, I end up getting stuck for large rates within Canada. For packages to the western provinces I was actually losing money on shipping.

The same item shipped using USPS could be sent with first class parcel which provides a much faster service standard and includes up to 4 times the insurance coverage as our postal system does (for parcel). At it could cost as little as $2 total.

It's possible for me to ship to the US for close to $2 but it doesn't include any insurance and takes at least a week. This is the method I was thinking about when I said that I could ship internationally (much) cheaper than within Canada. And lately, with faster (but not guaranteed) delivery times.