I buy a lot off of Ebay, including relatively heavy tools and books. Up until a couple of years ago, USPS parcel post was better for smaller parcels and UPS for oversize and over 25 lbs. Then USPS raised rates AND eliminated parcel post and 1st class parcel rate to Canada forcing shippers to use Priority International. Result-cost more than doubled. Now UPS was cheaper for anything over 3 or 4 lbs. And faster- 7 days to my location in Manitoba vs 10 days for Priority Mail. BUT all those comments about UPS's hugely EXCESSIVE brokerage charge for Customs clearing are absolutely true. The Post Office charges a flat $5.00 for 20.00 value & up; UPS min $15 to over $60. ,depending on value of parcel over $20. to around $300. Even front line UPS employees are embarrassed by this.(The actual duty/taxes assessed by Customs is on top of these fees & are typically 12-15% of goods' value).
HOWEVER, the brokerage fee can be reduced to nil by doing your OWN Customs clearing and UPS has helpful staff liason with customers doing this. The process is simple, but a little time consuming. If you live or work a long way from the UPS depot and/or a Customs office, the time and travel costs might make it impractable. 

Recommended: Yes