We have to charge the GST/HST on orders being shipped to backers based in Canada.
This is a legal requirement and the CRA (Canada Revenue Agency, equivalent to the IRS in the US) is very aware of Kickstarter projects.
We had an HST audit conducted on our company by the CRA in relation to the Catacombs & Castles Kickstarter campaign. We were able to avoid penalties as a result of us collecting the GST/HST proactively during that campaign.
They are monitoring the Canadian crowdfunding space, so we as creators MUST comply with the law.