Singular country names are written without definite article ("hotels in New Caledonia", "accommodation in United Kingdom",...) while pluralized country names are written with definite article ("newspapers in the United States and in the Balearic islands", "banks in the Netherlands",...).

What about country names such as "Dominican Republic" or 'Czech Republic" ?

"banks in the Dominican Republic " or " banks in Dominican Republic"?

"hotels in the Isle of Man" or "hotels in Isle of Man" ?
the ... Republic
the Isle of Man

The general reason is this.

'Canada' because there is only one Canada.

'The Dominican Republic' because there are many other republics and we are being specific.

Best wishes, Clive
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Many thanks
 Clive's reply was promoted to an answer.
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P.S. By the way, I would say "the United Kingdom".