Query for filterable, select by tag, show categories for filters

I have a CPT that I created called cars.  I have created custom taxonomy for categories (cars_category) and tags (cars_tags).  The categories are used for the type of document, and the tags are being used to identify the country the document originated from.

I want the filterable list to show the categories.  This works without any problems. Easy.

What I want to do is also have the list only show one specific country - so for example, the page would have the 5 or 6 filters at the top, but would only show results where cars_tags = USA.

I can use the post taxonomies & terms and enable the tags and select just USA, but then it shows up on the page as a filter.

I tried the advance meta query, but I'm likely not doing that right.  Any guidance with using it would be appreciated.