[Roadsters] question on shipping to Canada

[chalsted at comcast.net]

wondered if anyone from Canada could answer this one for me- I'm shipping a set of core seats with runners to Canada...USPS I have to ship in 2 packages as boxed together they run 69 lbs and I can only get USPS prices up to 66 lbs which I figure must be 30kg...will cost me about $150 just to ship the 2 packages. UPS will ship in one box for about $80 but the customer is adamant they want shipped USPS, says they will have to pay $60 in customs fees if sent UPS but evidently no customs fees if sent USPS...how can this be? doesn't make any sense to me. please enlighten me... 
Thanks 
Craig