Publicly asking your followers on any social media at all would only count as consent if you explain who you are, what they are consenting to, and tell them they can unsubscribe at any time.
We would avoid gathering consent using this method, as it can be risky, since comments can be deleted and so on.
Provided you treat it like any other consent form, you would be alright. If you haven't seen already, you can view a presentation on the ins and outs of CASL on our CASL page, as well as ask any other questions you might have with a member of our staff. And remember, burden of proof is on the sender. Should you choose to ask for consent using social media, you will have to be able to prove that you gathered consent this way.