CIC changed it's rules on Police certs. As long as your Police certificates are obtained after you left the country concerned..there is no expiry...I doubted this little gem, but my background check is in progress right now and my police cert was nearly a year old when I sent off the application, when they started processing it was 13 months old, so that kind of proves the point. I was planning to request a new one (takes 5 weeks from the UK and you can do the entire application online) as soon as processing on the sponsor started, this cert was just to "tick the box" so to speak to get the app off going on the old advice of "they like police certs to be within 3 months of the application date, and certificates are only valid for a year".
This is copied straight from the CIC website:
Who needs a police certificate?
In general, you and all the people in your family who are 18 or older need to get a police certificate. You must get one from each country or territory where you have spent six or more months since the age of 18. For example:
if you visited, worked or lived in a country for two months, left for a few years, then returned for four months, that counts as spending six months there. In this case, you would need a certificate.
For the country you currently live in, the police certificate must be issued no more than six months before you apply. This does not apply to us, being inland and already being in Canada
For countries where you have lived for six months or more, the police certificate must be issued after the last time you lived in that country.
If your certificate is in a language other than English or French, send it when you apply, along with the original copy of a translation done by a certified translator.
If you are Inland and you do not leave Canada since having the medical then your medical results do not expire either, the doctor that did my immigration medical told me that one.