There are a few reasons why the exact amount you'll have to pay is a little tricky to calculate. Firstly, it depends on what figure is actually quoted for customs declaration purposes. Secondly, the exchange rate used - the Canadian dollar is a bit stronger than it was, so this does work in our favour a bit. The other issue is what province the international deliveries actually LAND in rather than the province you live. In the above calculations I made the assumption that they would arrive in your home province but that might not be the case. If DHL main hub is in Alberta for example, then I think you would only pay 5% plus the processing fee.
It should be clearer once a few more Canadian orders trickle in; it seems to vary whether you need to pay upfront prior to actual delivery, or whether you'll be invoiced later. I've had both situations occur (sometimes it arrives months later a long time after I'd forgotten about it). The invoice for displaying what you owe does show the declared value, taxes and fees separately. So you'll be able to work backwards and figure out the percentages.