It is possible. The first thing Is to figure out what "announcer" you want to be. There are the emcee's and the game announcers. The emcees are more showy usually jumping around the field and such where the game announcers are either at a desk or right by the field never actually going on the field.
Once you figure out which role you want to try and get go onto VIMS.
https://my.usfirst.org/FIRSTPortal/L...IMS_Login.aspx
and you can apply to events.
Being Ontario is going districts I am sure you can find an event to volunteer at. Volunteering is a blast and I really recommend you do it. You are not going to get assigned as a GA for every event and it is actually possible that you wont be a GA at any event. Generally there is a greater need for Emcees (2 vs 1) so that is option.