Don't apply Round 3.
Also, you can afford to work at least 1-2 more years before applying. Simply put, while you have a good start to your career thus far, you're up against other engineers (from around the world) who will have more experience and more achievements to talk about than you. Most engineers at these top schools have around 4-6 years of full-time experience at matriculation.
And before you trumpet your co-op experience - don't. The only people who seem to make a big deal of it are Canadian students (mostly Waterloo and UofT engineers). Yes, it may be a big deal in Canada for a young person just coming out of school, but no one else around the world cares. They are considered internships, not real full-time experience, no matter how you slice and dice it (the big reason is that the expectations are MUCH different for someone who is hired full-time versus someone hired for a fixed period to work on a specific project). Also, when you have a few more years of full-time experience (when your undergrad and co-op experience becomes more a distant memory), you will be better able to put it in perspective and realize that it's not really the same as your full-time experience: in fact, you will likely find that it will take next to no space in your resume because you have much more achievements and milestones from your full-time experience to highlight.
Again, you have a solid start to your career thus far. Keep working. Don't rush into b-school just yet because at this point you aren't as competitive as other engineers applying. With a few more years under your belt you will be more competitive for b-school - not just admissions, but also post-MBA recruiting.
At the very bare minimum, apply for the R1 deadlines this fall -- not for the R3 deadlines now.
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