If you want to take maternity leave you have to tell them, in writing, *at least* 4 weeks before you intend to go on maternity leave.
I'm a cna and I told my work that I was pregnant as soon as I found out which was at 10 weeks. When I got to be 24 weeks I was put on weight restrictions since I was getting bigger and I work with combative residents
I work in a very small office and live the cubicle life, so it's hard to keep it a secret. I work as a probation officer so I told my boss at 5 weeks to ensure my own safety.
I live in Canada as well, Ontario. I don't think you are "required" to tell them at any time. I chose to tell my boss at 4 months pregnant so he could just start looking for someone else. Soon they'll be able to tell so it's up to you.
In my opinion u can tell them whenever u wan5. I told my job when I was starting to get a belly and when I was required to drink more water throughout the day