He just has to counter the governments initiatives and suggest why they are wrong and give vague guidence on what he would do until an election is called. The opposition does not put forward policy. Length of time is irrelevant.
Despite what I've read elsewhere I am willing to give the man a chance.
We'll see what tune he has now that he's leader, if it stays the same or shifts.
Regardless though, Trudeau needs to GTFO, but the other parties need someone electable.