Don't board xantids vs Canadian *****.

They don't have much of a clock to take you down, you just have to fight their counters and finish the job. It's tight game, and discard work better than them having use of their fire/ice.

You could trick out Dark ***** and Team america by playing xantids, sometimes it works since they board out removal, but it's a psychological war. How good are you on reading your opponent, will he be the kind of player that blindly boards out removal or not? the answer to this, is the answer to your boarding. just look carefully as your opponent is boarding. Tricked my opponent once with this and he ended up stifling my xantid 3 turns in a row before he died.

I'm not sure if I board against combo at all. If you play a duress ftw, and they chant, you take out 2 cards at once.
If they don't, check their mana, if they are not capable of going white, take iggy chain, if they can....ad nauseam.
I've won mulitple mirrors vs TES, because I kept any hand with a few discard, TES takes harder hits from discard than ANT does. We play more cantrips and can find/protect our business better. TES has the issue of not being able to sculpt their hands the way ANT can. This is an advantage that you really want to abuse. If not, win on T1 works as well.

Besides that, combo-mirrors are a dieroll anyways. You can hope you don't die on T1, and after that if you make a single mistake with duress targets, you lose as well.