Import duties don't depend on the point of origin, they depend on the country of manufacture. Same duty rate for new or used models. The USA is under the Canadian free trade agreement, so X5s have no duties. 3 series are usually German built, so they have duties.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue