Amazon affiliates with international traffic faced a big problem with Amazon: link localization. Each local store of Amazon has its own links and if you have visitors from Canada clicking on links from Amazon.com you probably won't get commissions. There were attempts for community to create localization plugins but there were many problems unresolved, such as different SKUs for the same product in different countries.
With the latest update, Amazon clearly wants to fix this issue. They released OneLink, a feature that will show links from local Amazon stores in Canada and UK for visitors coming from those countries, instead of showing amazon.com links. To do that, the affiliate accounts from Canada, UK and US should be linked ( they added this feature too ).
How it works ? You add a script in your website HTML code and it will automatically convert links from amazon.com to links to amazon.ca and amazon.co.uk, depending on visitors country.