I buy quite a bit from the States- Ebay and all that.
Have the shipper enclose an invoice as well as the declaration.
GST of 7% must be paid on Canadian value.
Provincial sales tax must be paid (none in Alberta, about 7% in other provinces)
No duty on musical instruments that I can find.
Be extremely about under-declaring the value. Customs can slap on a value or ask for an evaluation. They can confiscate (a lot of confiscated material is sold at auction)
$900 US = $1440 Can. 7% GST adds $100.80. On top of this, add the provincial sales tax. I est. abt. $1650 total.