Be sure to keep up to date on who is listed in your neighborhood. Within the last year, they have been adding Level 2 offenders, so in some areas the list has grown quite a lot. While it surely does not contain every sex offender, it is useful as a tool to at least be aware of the known ones. You no longer have to enter your name or address information. We can't protect our kids enough from these predators.
National US Dept. of Justice site:
Unfortunately, it looks like Canada has a national registry, but it is only available to police agencies. The information is not available to the public.
There is also an inmate lookup site for anyone who has been in a NYS prison in the last 30 or so years. Not to say they are sex offenders at all, but they could be violent and capable of other offenses on you or your family. Knowledge is power!