Instead of proposing ratification by the state legislatures, the federalist proposal called for ratification of the constitution by what?

Federalists proposed that popularly elected conventions should ratify the Constitution rather than the state legislatures themselves doing the ratifying.

In this way, state legislators were not being asked to vote for a document that would have them give up some amount of their own state authority.  Also, by having those who attended the ratification conventions be elected by the people in their area to represent their interests, the Constitution would be seen as having the full consent of the people because they had directly elected the convention delegates who approved the Constitution.