Officially, we need to pay tax for the electronic devices that we bought from outside Canada.
On the other hand, Canada is based on the honest system. Custom inspectors do not inspect every traveller.
If we bring a laptop outside Canada, we can fill in a form to declare that the laptop is presence in Canada before we go to the other countries. This form can be signed by the Custom officier in the Canada Border Service (previously known as Canada Custom) office in the ground level at Ottawa Airport.