It's worth remembering that, in the post-Tory mayoral byelection, city councillors were allowed to run without having to resign their seats. This is part of why people like Matlow and Bradford (and Anthony Peruzza, for that matter) ran despite having extremely long odds.
This will not be true in the general election. Incumbent councillors will have to choose between a mayoral run and a council run. Which is, perhaps, why Bradford is working so hard to put his name out there today. (He can change his mind about which race to enter right up until the filing deadline, so for the time being, he can have a flutter on the mayoral without risking his council seat. He will eventually have to decide.)
This is also why I expect Matlow will stay out if Chow is running. No upside for him to give up his council seat and lose the mayoral quite badly, especially if he becomes a spoiler for Chow and lets Tory or Bradford win. (Especially given that, if he wants to win the next mayoral race, he'll almost certainly need the support of the municipal NDP infrastructure, who'll remember what he did to Chow...)