In October 2013 I entered Canada from the UK (I'm British) and the guy at immigration stamped my passport, but wrote Exp Oct 2016 in pen under the stamp. I left Canada in Feb 2014, then re-entered Canada April 2014. They guy at immigration looked at the stamp & told me I'm good till 2016. He DID NOT put another stamp in my passport this time!
Does anyone know what this means? Am I good to stay until 2016? or do I still have to leave every 6 months?
You are allowed to stay for six months. If you want to remain longer without leaving Canada you should apply for an extension before your six month visit expires.