The Toronto Public Library has an annual contest where they collect work written by students who live in Toronto, ages 12 - 19,  and add it to their magazine, called Young Voices. Their written work submissions are preferably typed, though handwritten pieces are accepted too, and 1000 words is the limit.

You can also join their editorial team (made up of youth aged 12-19) and help judge the contest (though I believe you can't be a participant if you judge). You must contact their email address (linked on the site) to do so.

Scroll to the bottom of their site to see their entry requirements list

The TCTE Short Fiction Contest is a short fiction contest open to all high schoolers in the TDSB. The minimum word limit is 1000 words, while the maximum limit is 2500 words. This is a contest for prose fiction only; poetry is not accepted. You also require the sponsorship of an English teacher from your school (see full list of submission requirements in second button). 

If you're interested in writing for the TCTE contest, which has been running since 1985, click the first button below to be navigated to their home page