Basically, any enterprise in the US that is interested in doing business with Canadians will ship via USPS. Some of the larger corporations (LL Bean, LandsEnd, etc) have warehousing and shipping arrangements that let them avoid padding the cost with UPS etc charges.

If you are using one of the more expensive UPS services ('Air/Global/whatever') the 'brokerage charges' are wrapped into the shipping cost and don't appear as a separate item. This may explain your Nelo experience.

Also, the 'trigger point' for charging tax on USPS/CanadaPost shipments seems to vary depending on the season and parcel volume - sometimes a parcel will 'slip through'.....which NEVER happens with UPS ("Gotta get that $35, sucker!").
BTW, the dyes from Wood Essence are excellent! ;-)

Well let me mention that I paid the equivalent of $20 for the shipment from Portugal to Canada with UPS and it was still faster than any delivery I ever had from the US.
Thanks so much for all the explanation, I will try to go with USPS next time. The only unfortunate thing though is that no one seems to ship Hazmat-labelled items with USPS…

Since you mentioned the dyes: do you know anything about their UV-resistance? that was the initial reason why I went for the Behlen stuff since most dyes seem to fade very willingly.