The question may look a little bit stupid as a lot fo you would probably say: not a chance. But I personally believe that campaigns matter. On top of that, we've seen Stephen Harper in 2006 overcoming a deficit at the beginning of the campaign. Granted, his rise was mostly due to a re-alignment in Quebec, something not likely to happen anytime soon for the Liberals (or to any other party for that matter).
Another thing to keep in mind is that provincial swings aren't that big from one election to another, especially when the last election was less than 3 years ago. Yes the Liberals dropped from 44.7% in Ontario in 2004 to only 33.8% in 2008, but it took two elections, 4 years, a more solidified fusion between the Canadian right and a weak campaign from Stephane Dion. So, all in all, a provincial swing of 5-points seems to be the maximum possible between two elections.
The first thing to do to answer this question is to look at the current projections and apply the margins of error. But apply them to all parties simultaneously. In other words: I'll input the CPC and NDP at their lowest and the Liberals at their max. The results would be as follows:
Basically, it would be back to 2006, except for the Bloc. Now, let's look at the close races. The Tories would win 120 safe seats and be involved in 29 close races. The Liberals would have a potential of 84 safe+30 close races=114 seats. As for the NDP, it's 22 safe and 17 races. So, even by applying the MOE to get the best case scenario AND giving the Liberals all the close races they are involved in, they would still fall short of winning the election.
Even by giving the Liberals a 5-points swing in Ontario (they would stand at 39%, like in 2006) and taking away the same swing from the Conservatives (putting them back around 35%, as in 2006 as well), the Liberals would then win 112 seats, as opposed to 126 for the Conservatives. But at least, in this scenario, the potential for the LPC is 93+34=127, way above the safe seats for the Tories (108). One of the problems for the Liberals in order to regain power is the recent efficiency in the votes from the NDP. Indeed, if you use the model and input the percentages from 2004 (I might write a post about that soon), you see that the Liberals would win about 10 seats less than in 2004, simply because the NDP votes is now much more efficient.
So, the short answer to my question is: no. The Liberals can't finish first in term of seats. But if they are really up as much as the recent polls indicate in Ontario, we could well have a much narrower minority for Harper. Below is the best case scenario discussed in this post.