I know kayak offers a good feature exploring the flight ticket prices originating from different cities (obviously Toronto will be the city most people here care about), but other than selecting a defined month or spring/ summer/ fall/ winter, we don't seem to be able to set a more detailed dates (such as July 25- Aug 5). I wonder if anybody knows how to do your research exploring ticket prices and find deals when you know the rough time of your vacation but not sure where to go?

Oh kayak's app? If so, it does let you do date ranges I think. I put a date and use that date for several cities after some research.

skyscanner lets you do months, but I think you want to search with variable destination?

skyscanner is the best for variable destination for specific dates in my experience

If I wasn't being clear enough, or if people aren't familiar with kayak's explore function. I was referring to something like this:
http://www.ca.kayak.com/explore/YYZ/
http://www.ca.kayak.com/explore/YYZ/20151201,20151231/
So basically you have the clarity to see it at once. Checking all the good deals and see if any of them interest you.
Setting a date range and keep changing destinations to check the price isn't what I am looking for here, nor is typing in multiple destinations, which ITA can let you do so already.

Thanks Julian ! Wasn't familiar with sky scanner but will look into it!

May wish to read the responses to the post by Melissa Martinez Leo from about 1 hour ago.

Thanks Chris, I did notice that thread soon after; funny thing that I asked/ posted the (same) question first.
Actually I know Google flight explorer and was rather familiar with it, but it's not without flaws/ restrictions. One of the biggest issue for example is that I'm already looking into the vacation for Xmas-NYE period beyond 6 months from now but the latest info Google explorer is showing now is only up to Nov 15. So at least for the moment it doesn't help much (of course if I wait for another month when Google shows up the next 6 months flight price info then maybe it will.)

That is annoying, I know! Try this little trick. Edit the date at the end of the URL in your browser, and set it to 3 or 4 months ahead of the current date.
example: http://www.yyzdeals.com/img/ul/txuruvotg62jh337.jpg
^^ see on the right hand side, change it from 2015-05-27 to 2015-09-27
Unfortunately It won't load the complete data for all destinations, but it does load some.
YYZDEALS.COM
www.yyzdeals.com

Wow thanks again Chris!! That's a neat trick!! I changed it to 11-27 (to 09-27 it still won't really show up end of Dec deals properly) and now I can see a lot of European cities still at $600~700 range. Gonna do the same for a few other regions and I can decide my Xmas holiday destination soon enough!!

Now seeing 12/23 - 1/5 Tokyo at ~$860 range. Amazing! This is exactly what I was looking for! Appreciate for your help!!

At the risk of bursting your bubble, google flights explore is in $USD
Just in case that was a $USD price you were seeing.

That I know. But Xmas time at $1000(ish) CAD is still a pretty good deal for Japan.

Definitely! That's closer to the typical non-Christmas price, and Christmas often means 1.4 to 1.6 times the non-Christmas price.