As you've probably guessed, I keep a ton of spreadsheets around. One of them tracks every E3 purchase I've made since 2011. It also tracks the divergence from US MSRPs over time, to serve as a pseudo-baseline versus earlier on-par years (yes I know that's not accurate and you can't compare currencies that way blah blah blah whatever). Here's my average discounts over the past few years:
2011: 36.38%
2012: 33.34%
2013: 33.34%
2014: 39.76%, 33.93% versus US MSRP
2015: 32.71%, 15.06% versus US MSRP
2015 Black Friday: 30.68%, 12.93% versus US MSRP
2016 so far: 23.87%, -0.36% versus US MSRP
Despite the fall in the CAD, 2014 was actually one of the best years ever for discounts (thanks mostly to Amazon entering the fray).
EDIT: recorded the wrong prices for the $49.99 games this year, fixed the numbers. Now it's just slightly below par with the US, yay?