Hi ravindragollapudi,
First off, a 680/Q50 is a strong Score, so you are likely fine to apply to all of the Canadian Business Schools that interest you. The highest possible IR Score is an 8 (so I assume you meant to type that instead of a '9'); while that's a fantastic performance for that section, many Business Schools have publicly stated that they don't use the IR score as part of the application process. Most Schools expect you to be able to write a decently-organized essay in a short period of time (which shows your ability to communicate effectively with written words) - and to that end, most Programs would want you to score at least a 4.0 on the AWA. This 3.5 won't necessarily keep you out of any of the Programs that you plan to apply to, but the Admissions Committees will notice it. As such, you might want to write an additional (re: optional) essay or ask for an interview - so that you can better present yourself and try to 'offset' any concerns that this 3.5 AWA Score might create.
All things considered, a retest is probably not necessary. This is ultimately an Admissions question though, so you would likely find it beneficial to speak with an Admissions Expert about your overall profile and plans. Those Experts should be able to answer your Admissions questions and help define the specific areas of your profile that could use some improvement. There's a Forum full of those Experts here:
https://gmatclub.com/forum/ask-admissio ... tants-124/GMAT assassins aren't born, they're made,
Rich