I am a visitor and I would like to stay longer in Canada, can I go to the border and re-enter Canada to extend my stay?

Although some people like doing that, it is not recommended. The general rule is that a person who is a visitor to Canada must remain outside Canada longer than what they remain within. If trying to re-enter the country after several months of being in Canada there is a risk of being refused entry and removed to your country of origin. The best way to extend your stay is by filing an application on-line.