The two former ministers were removed from the Liberal caucus in early April.
Also says he would get tough on China and Russia.
Scheer revealed Sunday that he’d received a letter from Trudeau’s lawyer serving notice of a possible libel suit.
The NDP leader now faces an uphill battle ahead of the October election.
Worries exist over whether political advocacy groups will collude with parties.
Bernier announced in September that he’s starting his own party, the People’s Party of Canada.