(Canadian

Assuming CAD is your Home currency, you can try this (backup first):
- Change your home currency to $US
- Archive your $US account
- Change your home currency back to CAD
If you find anything not to your liking, restore the backup.
"How do you change home currency?"
I have the U.S. version of Quicken, so I can only speak for that.
Tools > Currency List.
Select the desired Home currency and click the Home button (near the foot of the List).
If you have the Canada Quicken for Windows version, you can try another approach: plan to turn your existing investment account into the archive account. It's not really the same thing as the new feature; but if you have been experiencing sluggish performance due to an investment account with lots of transactions, it could provide similar relief.
Manually create a New investment account with the correct currency.
In the old (the pre-existing) investment account, initiate a series of "Shares transferred between account" transactions (one security - one Shares Transferred transaction - at a time), to move the current holdings of the securities whose positions are still open, from the old account to the new account. All the transactions, as of the time you initiate the process, will remain in the old account. But you can continue tracking your open positions (and any new holdings) in the new account.