I taught it for years. It's true that for treatment in Quebec, the age of consent is 14 years.
In the federal Criminal Code, the age of 18 years is used everywhere. There is another criminal code for people under the age of 18. It's an age commonly used as a dividing line.
The intent was to completely prohibit these practices for young people under the age of 18, who could be pressured. We chose 18 years because it's consistent.