Let me start, but I may well want to defer to my colleague.
The general answer is that Canada is a member of the OECD and seeks to follow the OECD model. That's essentially the template or text of the OECD model tax convention. It's not that we follow in every respect the tax rates that apply under the OECD model. For example, the OECD might propose a general exemption from withholding tax on interest and royalties, whereas Canada reserves the right to impose a lower rate of tax but a positive rate of tax on such income.
Also, in the negotiations, the other country's position will be taken into account. They might want changes that diverge as well. I can also think of a couple of specific things that Canada seeks as part of its base negotiations. For example, since 1972 we've had a departure tax, a tax applying to people who emigrate from Canada, and it was strengthened quite a lot in 1996. To try to relieve double taxation, Canada has, since 1996, sought to have in all its treaties a provision to essentially step up the tax cost for the person moving to another country so they won't be exposed to double tax in that other country. That's an example of a divergence.
There are a number of those. We basically follow the model. I don't know that I could go through them all with their differences.