Shawbridge -- these are complicated questions -- I think artworks by a Canadian citizen and made in Canada can reenter Canada without duty/import taxes -- but then there is usually proof of export from Canada.

What did you do with the UK? Put up money for an import duty bond?

I do understand that smaller museums may not have the budget for international shipping. Perhaps the museum has worked with a shipper that has experience, even if the museum does not do it themselves.

It would be a major disappointment if the larger works were damaged/delayed by customs, as this exhibition is an important achievement for your wife.

I did look into getting a carnet for one situation, spoke with the company, who were very helpful, and made me realize that it was not appropriate. I absolutely agree with consulting a professional customs broker and/or shipping company.