Ontario is bigger than most European countries and as such the Bills cannot claim it exclusively for their own.
That said, the Bills can reasonably claim the Niagara region, St Catherine's and Hamilton.
There are too many bandwagon fans in Ottawa and Toronto for the Bills to claim these cities exclusively.
Ottawa is composed of many ex-Montrealers who fled separatist Quebec with Patriot loyalties. Ottawa and Montreal still have loyal CFL fanbases.
Still Bills fans loom large in both Ottawa and Toronto.
As you go west of Niagara Falls