we are not registered for provincial sales tax in BC as we do almost nobusiness there

no idea - I asked today, as I found another error in their calculation -there was no Alberta in the drop down either...

I spent about 45 minutes on Chat with Shopify - no real understanding of the issues (thought I was trying to set up sales tax), and said they would report my findings to their developers.  From my read of CRA, there is no sales tax 'holiday' for ship...