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http://www.trd.fin.gov.on.ca/userfiles/page_attachments/Library/3/Rsie_In43.pdf?N_ID=3
In Ontario, you should only pay GST. If you've been charged PST, your dealer is not looking after you.
It is very clear that if the tub is placed on a concrete slab there will be no RST charged or shown on the invoice.