Canada Anti-Spam Law: 3 Year Grace Period?

That three year grace period is if you can prove that you have an existing business relationship with someone. Here's one quote on this: 

"If they can demonstrate that they have existing business relationships with recipients, that counts as “implied consent” for a grace period of three years after the law goes into effect." (Globe and Mail). 

July 1st you can no longer send Commercial Emails (emails promoting your products and services where you cannot prove consent or a prior business relationship). To err on the side of safety, don't send anything. Here's the full Globe and Mail article (may help): http://www.theglobeandmail.com/report-on-business/industry-news/marketing/businesses-take-advantage-before-anti-spam-law-begins/article19252592/

There are some other discussions out there with what others have done to become compliant. Most are sending emails to their existing databse requesting an explicit opt in. Then setting everyone else as marketing suspended. Even on forms for gated content, it would be recommended to ensure that you are clearly stating that this is consent to receive marketing emails and offer an opt-out or in for that (depending on your wording).