RE: Multi-currency reporting - Displaying an Invoice in the local currency
For most of us GP peeps on here we think in terms of functional currency and originating currency which would be the more the familiar terms.
Question: you say "we pay through one of our companies using CAD" is that a separate company in GP that has a different functional currency or is this you pay one of your vendors you pay in CAD?
Assuming the latter:
If I have a company who's functional currency is USD (that's most of us) you then create relationships to other currencies (such as CAD) allowing you to enter, report on, and pay in a different currency than the functional (I believe this is what you mean by default) which is the originating currency in the transaction.
If you open you Transaction Entry window in AP you should see the Currency ID field. If you want to track a CAD transaction you need to enter it here with the Canadian currency. CAD becomes the originating currency, USD remains as the functional or base currency. You can toggle back and fourth between the two sets of values on most any window but the process starts with you entering the transaction in the correct originating currency.
This is out of the box functionality. That said, it's a tough setup if you haven't done it before so I'd recommend you get some experienced help on this. It's an ongoing task to manage the rate tables and account for gain or loss and I think it might be easier if you also setup a CAD checkbook to pay these but those details are beyond my experience.
It works mostly as you describe, at my company we sell in 12 currencies, we only pay in one though so haven't gone down that path yet but it coming soon enough.