In a story that ran in today’s National Post (and across the Postmedia chain), Jeff Davis delves into the issue of Ontario’s “backdoor gun registry”.
Davis explains that these concerns were raised following a letter circulated by Ontario’s Chief Firearms Officer:

Suspicion the OPP is creating a long-gun registry by another name was stoked by an April 10 letter circulated to all Ontario firearms businesses by Chief Firearms Officer Supt. Chris Wyatt.
In the letter, Wyatt says that according to his interpretation, the new federal legislation that dismantled the gun registry only requires gun vendors to stop collecting some information.
“Bill C-19 does not define record of registration,” Wyatt writes. “The Chief Firearms Officer is taking the interpretation that a record of registration is the registration certificate number or a firearms registration number, only.”

I am quoted in this piece, expressing the view that Ontario seems to be contemplating an end-run around Bill c-19:

Firearms lawyer Solomon Friedman says the letter makes it clear that Ontario police, who opposed the destruction of the gun registry, are skirting the new federal law.
“He’s using the backdoor by using his control over firearms businesses essentially to extort them into complying with a registry that the federal Parliament has rejected,” he said. “If you read between the lines, he says ‘I don’t like the law Parliament passed, and I’m going to subvert it and maintain a provincial registry.’ ”
The approach the OPP is taking, Friedman added, is a sneaky one.
“At least Quebec is honest, and is going through the front door, as it were, and litigated this in court,” he said. “The CFO wants to appear to be complying with federal law, but at the same time maintaining a hidden business registry of firearms.