n.
a radio show where listeners phone in to talk to the announcer.
This meaning of hotline is very closely related to the general meaning of a 'direct telephone link for a specific purpose' (see OED-3 1a.) and was likely appropriated to apply to radio shows which rely on telephone conversation and debate with listeners. This meaning is not specific to Canada, and in fact occurs much more frequently in the US (see Chart 1). The term is therefore North American and not a Canadianism as defined in Dollinger (2015c).
See also COD-2, s.v. "hotline" (3), which is marked "Cdn", Gage-3, s.v. "hot-line" (2, 3).
- 1968  Although the problems were not all rapid fire, Murphy's Law (anything that can go wrong, will) was clearly at work. In St. Jerome, Mr. Martin's overcoat disappeared from a hotel checkroom. When his schedule got behind again the following day, Paul Jr. had to fill in for his father on a hot-line show.
- 1977  Stephen Lewis is still very much on the scene, coming at us from all angles in the media. He is host of a daily hotline show for a Brampton radio station, working from a studio in downtown Toronto. (If you start the day off with a number of psychotics in a row, it's almost nice to get back to the caucus.) 
- 1989  What age would that be? Probably 18, the age when society reluctantly permits us to drink, drive, sneak into an X-rated movie, or commit matrimony.
That column appeared in the Toronto Star, but the heat it generated was such that a few days later it was the subject of Neil McKenty's popular hotline show in Montreal.
Reaction was fast and furious. One after the other, callers declared there wasn't a doubt in the world about the rightness of teaching religion to the young, and they seemed pretty well agreed that the sooner this instruction began, the better. 
- 1999  Opponents said the finding did nothing to bolster Wilson's questionable reputation for financial acumen. They sarcastically recalled his coarse denial, on a radio hotline show when announcing his candidacy, "But I didn't stiff a widow."
Wilson's wife, Judi Tyabji, re-established her right in the B.C. Supreme Court to have her three kids from a previous marriage home for the Christmas holidays. 
- 2008  Hotline radio in Vancouver is as diverse as the city. Traditional hotliners dominate the airwaves at CKNW, but there are also hotliners serving the Chinese and Indo-Canadian communities, in their own languages.
The foundation of most every hotline radio show is picking up on the news of the day and running with it. But the diverse voices in local hotline also pick topics that specifically cater to their own communities.
Harjinder Thind is a popular hotliner and news director at Red-FM, an Indo-Canadian station at 93.1 FM. 
- 2014  Instead of taking life's little roadblocks in stride, more and more of us seem inclined to overreact, without benefit of sober second thought or even civility, instead screaming at authority, venting on radio station hotlines and launching human-rights complaints. 
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Chart 1: Internet Domain Search, 14 Aug. 2012