What good are Canadian $1000 bills in the US?

From a commenter on a previous post:

One question Wolson missed to ask yesterday, is in what currency did Mulroney receive his third payment in New York? It seems to me that if it were in Canadian dollars, then it would [make] no sense to put them in a SDP in New York, since he or his family could hardly use them as such in the U.S.

If he started to convert all these $1000 Canadian bills into US currency, the bank would probably ask him questions as required under US law when large sums of cash are deposited or converted. If he did not convert the Canadian money to US currency, then how did he bring it to Canada? I understand that if one brings more than $10,000 cash to Canada, one must declare it to the customs officer.

Well, that’s easily answered: Mulroney has testifed that he left the money in the US. In his ethics committee appearance, he said he “integrated those funds over a period of time in [his] own requirements in the United States.” I believe he told the Oliphant inquiry they were dispersed among family members there. On the other hand,

if he received this last payment in U.S. currency, then how much exactly did he get? Was the exchange rate considered at the time of making the payment?

Good question. Was it $75,000 Canadian, or $75,000 American? Did that last wad of $1000 bills bear a picture of the Queen, or Grover Cleveland?

INSTADATE: But wait a minute: it says here that the US stopped issuing bills in denominations of $500 or more in 1969. Banks are supposed to immediately remove from circulation any discontinued bills they receive, and destroy them.

So they must have been Canadian, no? Canada only stopped issuing $1000 bills in 2000, “in an effort to fight organized crime and money laundering.” (UPDATE: The forensic accountants’ report to the Oliphant inquiry confirms what the fifth estate had already reported years ago — and I had forgotten: that Schreiber’s withdrawals from the Britan account were in round numbers of Canadian dollars: $100,000, $100,000, and two withdrawals of $50,000 each.)

So it’s a question that really needs asking: How on earth did Mulroney dispose of his Canadian $1000 bills in the US without somebody noticing?