Every floor-crosser that joined Macdonald's government came from the Anti-Confederation Party — a coalition of MPs mostly from the East Coast that sought to undo the formation of the Dominion of Canada.
That party collapsed during the first Parliament and its MPs largely dispersed between Macdonald's Conservatives and the Liberals. Anti-Confederation Leader Joseph Howe himself joined the governing caucus in April 1869.
What??? How could you invite people who wanted to undo your very country into a party after they fall apart.