OP = Original Poster
BTW (By the Way) I messed up.
First, I could be wrong on CiC for Canada
15. The Command-in-Chief of the Land and Naval Militia, and of all Naval and Military Forces, of and in Canada, is hereby declared to continue and be vested in the Queen.
Second, The Canada Constitution was passed in 1982.
Cruz was born under the previous British North America Act.
That makes Cruz a Natural Born Subject.
Cruz is a Canadian, and the Canadian’s have dibs!
Per the BNA, Natural Born Subject discussed
23. The Qualifications of a Senator shall be as follows:
(1.) He shall be of the full Age of Thirty Years:
(2.) He shall be either a Natural-born Subject of the Queen, or a Subject of the Queen naturalized by an Act of the Parliament of Great Britain, or of the Parliament of the United Kingdom of Great Britain and Ireland, or of the Legislature of One of the Provinces of Upper Canada, Lower Canada, Canada, Nova Scotia, or New Brunswick, before the Union, or of the Parliament of Canada after the Union:
Actually, Cruz had dual citizenship when he was elected, but subsequently relinquished his Canadian citizenship.