A. Trans-Siberian Railway- III. Russia
It spans across Russia and connects Moscow in the west to Vladivostok in the east, covering a vast distance across the Eurasian continent. 

B. Trans-Canadian Railways-IV. Canada
The Trans-Canadian Railways refer to the extensive railway system in Canada. It connects the Halifax from the Atlantic coast in the east to Vancouver in the Pacific coast in the west.

C. The Union Pacific Railway-I. United States of America
 The Union Pacific Railway is a major railway company in the United States.  It connects New York and San Francisco of the United States, and its completion was a historic achievement in the development of the American West.

D. The Orient Express-II. Europe
This line runs from Paris to Istanbul passing through Strasbourg, Munich, Vienna, Budapest and Belgrade. The journey time from London to Istanbul by this Express is now reduced to 96 hours as against 10 days by the sea-route. 

So, the correct answer is option 2: A-III, B-IV, C-I, D-II.