The extra charges are Canadian duty (on any item valued over $20CDN /about $16 USD) Canadian sales taxes (from 5% to 15% of the selling price of the item) and a ~$5 service fee to Pitney Bowes which runs the GSP.
The duty and sales tax are required* on any import over that $20.
The solution is not to buy anything valued under about $100CDN from a seller who insists on using the GSP.
It has been my experience that it takes about 20 days for a parcel to arrive from the USA, with or without the GSP being involved.
*CBSA and Canada Post have come to the conclusion that it makes no sense to assess and collect these import fees when the cost of the public service doing so is higher than the amount that could be collected. But private companies like PB and UPS are legally required to do so, and most collect service fees of $25 and up to cover their costs.
