If you've got zOS and COBOL knowledge then Toronto is the place for you. IBM develops their zOS software in Toronto (well, Markham) mostly. At least the compilers, DB2, and parts of WebSphere.
The other users are the major banks, and they're all headquartered in downtown Toronto. They're desperately looking for people with zOS and COBOL knowledge, I get plenty of recruiter emails for that despite not really having much COBOL knowledge.
Honestly, if you apply for any of those jobs with even a passing familiarity of COBOL you're pretty much guaranteed. Also, welcome to the mainframe club!