The notion that the French can apply pressure to the British by granting a short European Union extension won't work, because it will prevent going for a General Election. The way to get a result (Dear France) is to be counter-intuitive, which is to grant a very long extension, one that can absorb a General Election in the spring and a possible second referendum also in the spring, either one coming before the other. Also a very long one means the EU can look elsewhere for other pressing issues.
The way out of this trick is to be observant and nifty and abstain among the opposition, even if the opposition introduce such a vote, so that the move is made to a fortnight's effort to find a new Prime Minister.
Best result = Removing Boris Johnson and a new cross-party PM to negotiate with the EU
Second best result = Boris Johnson caged in as now
Worst result = Boris Johnson left in power as Parliament is dissolved with use of monarchic powers to negotiate and enact on EU matters, breaking conventions.
Jeremy Corbyn would have first shout, but then the Prime Minister job would fall to another senior back bench Member of Parliament This is the best way to proceed, for it would remove Johnson and put in a 'grown up' to run the government. The extension could then be as long as the temporary regime needs and wants.
Meanwhile, the Liberal Democrats must take advantage of Brexit fatigue, by pointing out that if we leave one way or another, the whole Brexit thing will go on, with a trade deal to be negotiated and another no deal cliff edge approaching. The Liberal Democrat campaign is then to be to stop Brexit completely, to end the nightmare.
A long extension may also have other results. More MPs might cross parties. Jeremy Corbyn may well resign, probably for a female left-winger. He would do this as at least in an attempt to start to prevent Labour shrinkage at the next General Election. At the moment he wants a General Election when many Labour MPs do not.