Security as US missions varies according to the threat. There are certainly no marines at the Consulates in Vancouver or Toronto.
As for extra-territoriality, the answer is yes, and no.
The PFI station is still Canadian territory. Canadian law still completely applies, and Canadian police still have jurisdiction.
The Preclearance Act, which is not yet in force, provides for (inter alia):
The administration of preclearance laws (US laws in relations to cutsoms, immigration, public health, food inspection and plant and animal health.) Preclearance law includes monetary penalties, but nothing that would be considered criminal in Canada.
Administration of preclearance law is subject to the Charter, the Bill of Rights and the Human Rights Act.
Where a candian offence is committed in a preclearance area, and charges are laid, those charges will take precedence over any US penalties that could be imposed, and the US penalties cannot be imposed.
A preclearance officer must not use force that is intended or is likely to cause death or grievous bodily harm unless the officer believes on reasonable grounds that it is necessary for self-preservation or the preservation of anyone under the officer's protection from death or grievous bodily harm.
American officers will not be authorized to conduct strip searches--those must be performed by a Canadian officer, and both the Canadian officer and a senior officer must have reasonable grounds to believe that it is necessary.