Honestly, I'd say to get a lawyer. The answer depends on a ton of things. Slipping up on any of them can cost you lots of time, money, and pain. You need to talk to someone who's trained to handle this sort of thing.
I mean, which nation(s) are you a citizen of? What nation's passport do you have? If you're not a citizen of Canada, what's your immigration status? Are you on track to become a citizen there? If you're a citizen of Taiwan, do you care about keeping that citizenship? Those questions can wildly change what you need to do.
I'm not a lawyer, and I'm from the US, so this may not apply at all. Here, if you're a naturalized citizen, you get a Certificate of Naturalization. If you're not a citizen, but on track to become one, they give you other documents. AFAIK, those documents serve the same legal function as a Birth Certificate. If you were here, you'd be wanting to change those documents. We've got separate procedures for doing that, and it doesn't seem like any of them care about whether your birth country recognizes your new legal sex. Canada, of course, could be different.
If you are a Canadian citizen, or are looking to become one, you need to be talking to an immigration lawyer now.
If you're not trying to become a Canadian citizen, or want to keep Taiwanese citizenship, your best bet is the Taiwanese consulate. And a lawyer.
Notice a theme here? Talk to a lawyer!
