Not a chance we'll see Trudeau step down before the election. We're eight months out, we're about to enter a really gross and protracted campaign... SNC is going to be a weight around his ankle, but at present there's no smoking gun for anything illegal, and even JWR characterized is as not illegal. This won't sink the government, it will just make te election suck more for them and will firm up some voting intentions while swaying a limited number of others. I don't think many votes will actually really swing on this over the course of the entire campaign.
That said, the election looks pretty set to be a toss up at this point, with the usual 'anything can happen' caveat.
Would Trudeau step down if the LPC win a minority? Probably not- if he can weather this storm he'll probably keep the helm. For a Liberal leadership replacement we would probably need to see a CPC victory.
There's really not a lot of name recognition outside of the top half of Cabinet. Freeland immediately jumps to the top of my mind - she has stickhandled foreign affairs, particularly with the US, about as well as could be hoped. Being orn in Alberta wouldn't hurt her much, and she has good business experience- I think she's firm grounded in the 'real world' when it comes to trade and finance. Goodale has the political clout to potentially put it off, but I think people would be looking for someone a bit more fresh... That said, he is very highly experienced in Parliament and in the senior levels of the party, and that has something to be said for it. He would avoid many of the missteps that have plagued PMJT.
Outside of those two, nobody really stands out, though several have kept their noses suitably clean.