The issue could be the ROE conversion that was used by QB. 

Are you able to view what entry/entries are causing the open balance amount of 120.46 CAD? 

For one of my credit memos the ROE didn't match the invoice it was to clear so even through the USD value was good the CAD equivalent was off.  Once I figured that out I was able to update the ROE used for the credit memo entry so that it would clear out the correct CAD value.