Interesting set of changes really put a lot of latitude on CPB in assessing potential travel to the US. The thing that seems most alarming is that Canadian citizens no longer have the right of withdrawal. Add to that this increase of powers.
U.S. officials can now carry sidearms in these preclearance zones, conduct strip searches, record and keep passenger information, and detain Canadian citizens.
Even if a Canadian official is (unwilling) to conduct a search or has deemed a detainment unnecessary, a U.S. official can override that call. In other words, Canadian law enforcement can now be countermanded within Canada by Americans.
https://www.cbc.ca/news/opinion/opinion-border-crossing-rights-1.5382547