Depends which side of the Liberal Party.  The progressives who swung over to Trudeau would never vote Conservative no matter what but certainly could swing NDP.  I agree amongst the Red Tories and Blue Liberals Scheer is not the best choice, nonetheless if Liberals are bad enough you have seen more right wing ones like Harris and Harper win over those types, but it tends to usually be temporary not long lasting and only if the other side is really bad.  Otherwise if running for premier of Ontario he might be able to win as Wynne is so hated, but it's unlikely Trudeau's approval ratings will be in the teens like Wynne thus relying on the Liberals to defeat themselves might work in 2027, but not 2019.