I would like to have my daughter's birthday in the park with 30 people in May 2021 !!! what do I need to do?

Reserve your spot , either early in the morning. Or get a permit from city hall.

I think areas like park tables and grills are first come first served. I've seen alot of large group bbqs in the summer with their own set up. But im sure with Covid, things may be a bit different now. The area by the lake with the boats and playground/play fountain is nice but im sure would be crowded too by the summer (or not cuz, again, covid...) But if you want to host it like at the rink, that you'd have to call. (there's a playground & court by the rink too and more open space right there & across the street too.) Public bathroom too (not sure now tho because again, covid lol) I'm sure the number is online and there's the electronic bulletin too at the entrance by the diner on St.georges ave.