I just got an email from WSIB stating that they just started a new program, which offers liability coverage:
"Through The Chubb Group of Insurance, WSIB offers Drivers Liability coverage for you while you are on track in declared events such as DE, HPDE, Member Days, Autocross, Time Trials and even Club Racing. This policy would cover damages to the track, another vehicle and others. With coverage is based on the number of event you participate in annually. "
Disclaimer: I am not affliated with WSIB.