OTTAWA—The Senate is urging the country’s top court to dismiss Sen. Mike Duffy’s challenge of a ruling that prevents him from suing the upper chamber for suspending him. In a submission to the Supreme Court of Canada, lawyers for the Senate say the legislative body’s actions are protected by the time-honoured bounds of parliamentary privilege. They argue privilege plays a vital role in maintaining the separation of powers between the legislative, executive and judicial branches considered crucial to Canadian democracy. The Supreme Court is slated to decide this morning whether to hear Duffy’s appeal. Duffy is seeking $7.8 million in damages from the Senate, RCMP and federal government following a high-profile investigation of his expense claims, which culminated in the Prince Edward Island senator’s acquittal on 31 criminal charges in 2016. Duffy was named to the Senate on the advice of then-prime minister Stephen Harper in 2008, but he left …