There is no general crime of prostitution in Canada. However, many of the activities that are usually associated with prostitution are classified as criminal offences.
For starters, buying sex from or communicating about buying sex with someone under the age of eighteen years is an indictable criminal offence that carries with it a minimum six-month jail term.
While it is not a crime in general to arrange to buy sex or communicate for that purpose, if this is done or attempted in a public place (eg. on the streets) it is considered a criminal offence. This is classified as a summary conviction offence.
Engaging in sexual acts in a public place is also a criminal offence that falls under the indecent act provisions of the Criminal Code. Even if you are engaging in sexual activity in the privacy of your car, you could be charged with this offence.
Obviously, the activity of prostitution has to take place somewhere. Again, the exchange of sex for consideration is not criminal, per se. However, if the activity occurs in a place which is used regularly or habitually for the purposes of prostitution, then it is considered a common bawdy-house. The Criminal Code makes it an offence to run a common bawdy-house, to work in one, to allow one to be operated over a place or premise which you have control, or to be found in one without a lawful excuse. Its even an offence to offer to take someone to a bawdy-house!
There are also criminal offences that deal with the other business aspects of prostitution as well. The activity of pimping is characterized as living on the avails of prostitution and is a criminal offence that carries a jail term of up to fourteen years in certain circumstances. Other procuring provisions also make it criminal to induce, persuade, or force someone into prostitution both in and out of Canada.
Its true that prostitution itself is not outright banned in Canada as a crime. However, there are a mine field of criminal laws that capture the many activities that often go hand-in-hand with it.