We were discussing on another thread aspects of these rules. It is a complex question, the rules appear strewn throughout different legislative sources. I cited in that thread the Food and Drug Act (Canada) regulations concerning the definition of whisky and Canadian whisky. Under these rules, no distillation proof threshold is provided. I could not find any other rule that stipulates one.
As for the 9.090% rules, I find this extract helpful:
I interpret this to reflect underlying rules (again they are in different places) that say two things: first, if whisky from Canada contains more than that percentage (9.090) of imported spirits (bourbon, say, or Scots malt), it cannot be certified as Canadian whisky on export and the certificate of age and origin accompanying it must in that case state what the respective percentages of domestic and imported spirits are. In practice therefore, all Canadian whisky (so certified on export) sent out of the country will not, as I read this, contain more than that percent of imported spirits.
Second, for the age part of that rule, if any domestic or imported spirits or wine are added to spirits (including therefore Canadian whisky), provided the absolute alcohol of the addition does not exceed 9.090% of the total alcohol in the blend, the blended spirits can be stated as aged for the period the spirits to which the addition was made were aged.
Thus e.g., if you add 2 year old 80 proof US bourbon to 6 year old 40% ABV Canadian whisky, and the bourbon represents 5% of the total blend, that can be sent out for export as Canadian whisky aged 6 years.
That is how I read it anyway.