Focus on your grades. Then focus on crafting the best application possible before submitting. Then focus on OCI prep. Then focus on in-firm prep.
This year's recruit seemed to be a bit different, but historically, and still to some extent this year: a B+ average at Queen's is good enough for atleast a handful of OCIs. I'm sure Ottawa is similar, although there are less OCI spots (40 vs 20 for most firms). Your corporate expeirence, should you articulate them well in your application, will proabably help you with getting OCIs.
At the in-firm stage, grades seem to matter less, but still matter. Your resume obviously still matters, but alot of it boils down to how much you can "connect" with a firm and your ability to interview/conversate. Remember they want to know if they can stand being in a room with you for extended periods of time. This is why some top students strike out and some average/below average students get top jobs. Very subjective process.
In my experience, networking is more for you to learn about firms than vice versa. Instead of helping me get OCIs, networking helped me convey my interest in firms during interviews. I don't think just slapping an articling students name on your cover letter will get you an OCI.
Don't worry too much about where you're working this summer. If you can pick up something solid that could improve your application (business/corporate/client-facing/law firm in area of interest), then thats a plus. But if you have good corporate experience through your undergrad and if you've been active outside the classroom during 1L, don't fret about not doing much this summer.
You're right - you want to try and make yourself stand apart from other candidates as much as you can. A lot of that boils down to how well you can articulate your experiences and relate your skills to what firms are looking for in your application, then in an interview. Focus on your strengths on your resume. As you get further along in the process you'll start to understand this aspect more (hopefully).
It's a marathon not a sprint. You have ample time after exams to prepare your applications. I very much understand how you feel because I was there one year ago! R E L A X