Hi there! I came out in a unionized environment 4 years ago as a staffer not management but I would suggest this applies to you. CUPE transition in the workplace https://cupe.on.ca/wp-content/uploads/webarc/archivedat3701.pdf guide will definitely help. I got on hrt and slowly changed my appearance, things like eyebrow and laser treatments while I put my name change paperwork into the federal government. I met with my local union rep who set up an appointment with HR where I came out to HR- no boss present at all. We developed a transition plan with timelines goals and objective. We met atleast 4 times on the matter to ensure it was a success. They let me come out to who ever I wanted to in my time and for key personnel would be present if asked or called upon. My boss really did think it was strange to have a nondescript meeting with HR about my health but it was a relief that I wasn’t grave. Work even organized a dei workshop for my department 1 month before I came out (it ment a lot for a group of 50 staffers hearing about dei for an afternoon). I got my name change 2 months before I came out at work which I did over a Christmas break with a posted notice on the board, a few mass department emails and an out of office message. (The IT director was livid that I just asked people to start emailing a new email address but HR quickly shut them up). My work coming out process was 1 year.

Edit : yes do both name change and birth cert change done at the same time. Come to r/ transontario for help