Are you doing payroll in both?

Ideally yes, but not necessarily.

In Sage 50 Canada, only when you start a new company, you have the ability to pick the home currency.

Sorry Dmaster, I should have been more clear.  I have a Cdn company and  USA company and will record transactions in both companies and when I tried to use the command, "File New" to create a new US company I see I really couldn't create one, it was all Canadian nomenclature.  

That's the reason for my question then would I then have to buy a Sage 50 US Version in order to create transactions and use the software for my US company then?

From a licensing standpoint, you need a separate license for each named user.  

It depends on how complex the two companies' operations are.  Compared to buying a separate software package for each country, it may require too much manual work to keep track of sales taxes, issue government forms, track payroll, etc., in software not designed for that country.

When Simply Accounting had both a U.S. and a Canadian version, there were numerous data fields that were in the U.S. version that just don't exist in the Canadian one.