I wasn't able to make out the company name of the caller, but he indicated that they are licensed by the Ontario Power Authority to call pre-qualified HVAC customers to register them to receive a rebate of up to $650 based on the efficiency of their HVAC equipment.  According to the caller, I wasn't going to have to buy anything because my furnace wasn't very old, but someone would have to come out to check the codes on my furnace before a rebate could be issued.  Apparently there was an information sheet included in either my electricity or gas bill last month describing the program.  I don't remember seeing it, but I may have tossed it after a cursory once over.

I told him I wasn't interested in having anyone come to my house, at which point he said 'okay', didn't push the issue and wished me a good evening.  Upon searching the internet I found http://www.powerauthority.on.ca/conservation. At the bottom of the Consumer Programs/Eligibility page (https://saveonenergy.ca/Consumer/Programs/HVAC-Rebates/Getting-Started.aspx) is a note indicating, "The Independent Electricity System Operator (IESO), formerly the Ontario Power Authority (OPA) does not call consumers to solicit participation in its programs."

Looks like the rebates may be legitimate, BUT the folks calling may not be authorized to do so.