Originally Posted by terenz
Indeed. Always remember that even if you pre-clear, you are still on Canadian soil. If the U.S. agents try to arrest you, detain you or in any way (attempt to) intimidate you, remind them politely you are on Canadian territory and withdraw your application for entry into the U.S.
Wonderful in theory, but in practice my experiences are very different. As you may be aware, in 2002 I was detained at YYZ PFI for 3 days by US officers and "interrogated" for 17 hours. I was denied access to contact my family, contact my lawyer or to contact the Indian consulate in Toronto - all in direct violation of the US-Canada Preclearance agreement. When I requested to be allowed to leave in accordance with Canadian law, I received a kick in the groin for my efforts and an order to "Shut the f*** up". It took me over 2 years to receive an apology from the US State Department for that incident and the Canadian authorities were also unwilling to pursue the matter due to issues of "procedural immunity" for US officers on duty.