There was indeed a 'bit of hooplaw' about these and every other 80% recevier frame some months back. These are now just like a firearm and need to be registered with the RCMP (as they are restricted, any non-restriced 80% doesn't) within X days of import. Now, as they don't come with a S/N the RCMP issues a F.I.N. number to the importer who has to mark it within X days. So these would be sold and transfered to you just like a G19 (but using the F.I.N. not the S/N) but with only a F.I.N on them, you still get to choose the S/N, mark it and update the RCMP once you've done that.
As far as anything prior to this change you'd need to ask the RCMP.
Scott