Echoing the suggestions from others, don't mention being trans or strangeness at being best (wo)man. You don't need to explain yourself or anything, just talk about your friendship with the groom, the happiness you've seen in the couple, talk about things they share that make them such a strong couple, and if you wanna bring some humour you can always share a story that might (lightly!) embarrass the groom but that you can use to maybe highlight a positive quality he has or talk about how he's grown since then.
Your role there is to give the guests some insight from a close friend into the couple's relationship and how special it is, and to help the newlyweds feel the strength of their relationship as they solidify it with their marriage. You can talk about yourself if it genuinely comes up in what you want to say, of course, but only if it's something that's ultimately more about the couple.
Do you have any recommendations for Canadians? I recently moved back to Canada from the US and now that I'm trying to actively avoid buying US products I feel like I'm figuring out my routine from scratch again 😅