Sure.
On Search any seller using the GSP has this note
Customs services and international tracking provided
Just avoid those items.
Also since only sellers shipping from the USA can enroll in the program, you can order from Canada, Europe, Australia, even Asia without the GSP charging you the appropriate duty and sales taxes in advance.
For what it's worth.
Duty and sales tax are applicable on almost any purchased import over $20, and any gift item over $60.
Duty is charged based on country of manufacture not country of purchase.
Canada Post charges about $10 to process these fees. PitneyBowes /GSP charges $5. UPS and other couriers charge around $25. These are minimums and will rise if the item imported is more expensive than $20.
If you are charged duty and tax on an item under $20, you can appeal to CBSA for a refund.