Cities can resist, but ultimately will suffer greatly if Ford decides to cut off any funding until they comply.
All he'd have to say is something like "without your support, cities will lose out of funding that can help ease traffic, improve schools, and pay for hospitals", and he'll have enough of the voting public on his side to force municipal leadership to cave.
There's a protest coming up for this too (as well as to remember those killed and injured):
On Tuesday, October 22 join the active transportation community to remember those people using active transportation who have been killed or badly injured on Ottawa's roads in the past several weeks, and to protest Queen's Park's anti-cyclist proposed bike lane law. Meet on the north side of City Hall at 110 Laurier Avenue West at 5 pm for a rally and then protest ride.