The Preclearance Act has been passed by Parliament, and has received Royal Assent. However, like most legislation, is provides that it will come into force, "on a day fixed by proclamation." When the Government has its ducks in a row, it will advise the Governor-General to issue a proclamation that the Act will come into force on a particular date.
The text of the Act (along with most other Acts and Regulations) is available at the Justice Canada website (http://lois.justice.gc.ca/en/index.html)
The Act does not provide for the carriage of sidearms, though it does presume that there are cicumstances under which US officers will use force in preclearance stations. It remains to be seen whether (and how) the Government will go about authorizing US officer to carry sidearms.