Today, it is official Bernier has been invited. Personally I think that is a mistake as the party hasn’t won any seats in a general election and is polling in the low single digits. My view has always been parties either that won seats in last general election or by-election or polling at more than 10% should be invited and Bernier meets neither.
As for impact, a lot of Liberals are cheering while Tories are worried, but I think many over emphasizing its impact. Campaign will already be three weeks into it by then so not a lot of runway time wise for big shifts. Never mind Bernier may just make Scheer look more moderate as while Scheer is too right wing for a lot of Canadians, he looks quite sane and moderate when compared to Bernier who is off the scale crazy right wing. If you look at past elections when parties that far back were included in debates, usually it has little impact. David Khan was in most recent Alberta election debate but still got only 2% and zero seats despite a decent performance. Most on right loathe Trudeau with a passion and defeating him is more important than electing their preferred leader. In 2008 Elizabeth May was included yet has little impact on final numbers. In 2013 in BC, John Cummins had a disastrous performance and fell from 12% to 5% and in many ways it was this disastrous performance that allowed BC Liberals to get re-elected. Bernier is much lower so has little room to fall, but a disastrous performance could cement his low numbers. The only case I know of a party well back taking off was Gordon Wilson in the 1991 BC debates who had the famous one line zinger “this is why we never get anything done in politics” and his party jumped from 12% to 25% overnight and ended up with 33% and official opposition and as they say the rest is history. However, there was a strong void that needed to be filled then which was those who wanted to get rid of the Social Credit, but didn’t want to elect the NDP. Federally I don’t see a void that Bernier can fill in.