给你个官网链接，说是要看航班时间 https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/transit/without-visa/china-transit-eligibility.html这里划重点，由你航班抵达时间是否在美国海关机工作时间决定arrive during business hours (hours may vary at each airport) for the preclearance area run by United States Customs and Border Protectionif you arrive outside of these hours, you will no longer qualify under this program. You will have to go to the Canada Border Services Agency to be screened. You should check your flight connections with the airline.
