Quoting the info blasted sabre found:
The holder of a small game licence may not use a rifle of
greater calibre than .275, except a flintlock or percussion
cap muzzle-loading gun, for hunting small game in
the counties of Brant, Elgin, Essex, Huron, Lambton,
Middlesex, Northumberland, Oxford, Perth and
Wellington and the regional municipalities of Chatham/
Kent, Durham, the former regional municipalities of
Haldimand-Norfolk and Hamilton-Wentworth, Halton,
Niagara, Peel, Waterloo and York and the City of Toronto.
The regulations state a .275 caliber, being as the 270's bullet is .277, I would be careful of a fins and feathers officer having a bad day and using you to make him feel better. Common sense says a 270 is smaller than 275 but some of the officers throw common sense out the window when it comes to writing up tickets. Just my $0.02 on that based on a different situation I've had occur to me.