Shipping USPS from the continental USA to Canada or vice versa is $30-$45 depending on the weight and volume of the package. Average in my experience is closer to $35-$37. Sending the same thing by UPS is $45+.
Brokerage fees and taxes for a uke coming into Canada by USPS amount to 10-20% of the cost. Brokerage fees and taxes for the same package coming by UPS can be 60% or more of the cost. (Yes! I paid $60 in UPS blood money on a $100 used uke coming from the USA this year).
So: A $100 USD uke coming by USPS costs $100+$30 shipping+$20 taxes and brokerage fee = $150 max.
The same uke coming by UPS = $100 + $40 shipping + $60 brokerage = $200 cost.
The moral: ship USPS, not UPS when crossing international borders.