Possible Clues:

• Ontario Port
• Capital suggested by the circled letters and by the starts of 17- and 63-Across and 11- and 29-Down
• After end of red, finished port...
• Road signposted by Milne
• Bird on river in port
• Bird above river where there's a castle
• Duke has superior way of passing port
• Cinque port
• Duke has finished the port
• Cinque Port