Toronto defamation lawyer Gil Zvulony was quoted by several media outlets with respect to the Rob Ford and Sara Thomson dispute.  He was asked whether some of the public comments crossed into defamation territory.  You can read a National Post article here and a Global News clip here.

Gil Zvulony spoke about how, in defamation lawsuits in Canada, the falsity of the statement is presumed.  If someone is going to defend a defamation lawsuit based on truth then the onus is on them to prove the truth.

Therefore if Ford wanted to sue Thomson for publishing the statement that he groped her/sexually assaulted her, then Thomson would have to prove that it actually happened.