Thanks for the rec on Glutinos - when they have the mint Girl Guide cookies here, I'm bad and cheat on my diet!
In Canada, while I don't know of any MtFs in Girl Guides (I didn't know of any trans kids growing up, period), I do know that they let girls into Scouts, though it was mostly boys, at least what I saw back then. Didn't know this until I was old enough to babysit kids in it, though, else had I been given the choice, I'd have likely joined that instead. You can see on their website that Scouts is quite openly not gender specific, here. The Girl Guide site doesn't say anything about trans girls in their FAQ, so I don't know what their position is, but cookies are released in the fall here, and not knowing anyone in it, it's so hard to get my hands on any!