Once an account is labeled CAD, it cannot be changed. A new Bank type Account must be created, selecting US $ as the Currency.
To utilize the Multicurrency function correctly, an Exchange Gain/Loss (Expense type) account must be created in the COA.
Then, from the Company tab on the main toolbar, select Manage Currency>Currency List to create a list of currencies used (in your case US $). Next, record (or download) the current exchange rates.
To record a transfer from your CAD bank account to US $ bank account in QB, use the Transfer Funds function from the Banking Menu. Be sure to include the applicable exchange rate. The exchange variance will automatically be recorded in the Exchange Gain/Loss account.
If the US $ account will be used for transactions other than bank transfers, corresponding US $ accounts must be created. For Instance, if payments will be made to US Suppliers, a US $ Accounts Payable Account must be created as well as Vendor Profiles with US $ selected as the Currency used. Same principle applies to Customers and A/R.
You should be aware that although the accounts are now correctly set up, most reports will only be reported in your Home Currency, but can be customized to display US Funds if necessary. The Balances in your COA are displayed in the Currency of the Account.