Everything on the website is setup to charge in USD because the majority of users are located in the USA and most production/shipping costs are in USD.
A Canadian version of the website is planned in the near future. It will charge CAD and should help resolve any currency conversion issues. However, it is not ready at this moment.
If you are located in Canada, you can voice your opinion regarding the matter or check on the status of the Canadian website via the general support form.