It is actually a lot simpler than you think. Actual costs fall into very narrow categories. Make canadapost.com yer friend:
http://www.canadapost.ca/cpotools/apps/far/personal/findARate?execution=e2s1
I use flat rate for USA, Canada, world based on weight. Sometimes I make a $. Sometimes I lose a $. I use price pointing anyway, so, it doesn't matter.
Get a scale and a tape measure.
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